radatats

no like I said before, its just a 2 channel amp so all you can do is change channels or turn reverb on/off with a footswitch.  If you want to control those other functions get an HD500.  The DT was made to integrate with it.  You could also do what you want with midi if you can program it.  Unfortunately that actually changes your DT so it will remain in the last configuration you sent it for that voicing.  The HD500 does not make any permanent changes to the DT and all your settings are saved with the patch in the HD500.

Here's what you do.  On each path right before the IR add a Volume gain block and pull it down to create a parallel path.  Drag the merge blocks down too so you have separate outputs on all 4 paths (1A, 1B, 2A, 2B).  Set the output block on the paths with the IR to XLR panned the way you want.  Set the output blocks on the no IR paths to 1/4 centered.  Now run your Left 1/4 out to the DT return and both Helix amps will be merged to the DT.  If you keep your post effects like delay and reverb only to the PA you will have a sweet wet/dry/wet rig.  Up to you.
 
As long as you are running into the FX return the DT preamp/cab is totally bypassed anyways so you shouldn't need any tuning that way.  I'm not wasting any time or money trying to match or beat my DT25 with anything you mentioned.  The only thing I am considering is the Orange Rocker 32 which has a true stereo power section.  No rush to get it though...

The problem is that even though the DT and the Helix use the same communication protocol (L6 Link), their basic software architecture is totally different and do not integrate.  They never will.  What you are experiencing is well documented by me and others here.  The Helix signal is actually running through the DT internal amp and cab models and that sucks.  The only solution is to also use a midi cable to connect your DT in addition to the L6 Link.  The Helix can send midi commands to the DT to control it.
 
You can program each Helix patch to configure the DT the way you want by midi and that works OK.  However, the DT will stay in whatever configuration you last gave it so I found that unworkable.  I found the best way to work it is to turn off the internal amp and cab on all 4 voicings on both channel A and B in the DT.  I then configured the 4 voicings in channel A to Class A, topology I-IV and channel B to Class AB, topology I-IV.  Now all I have to do is send one midi command from Helix to pick the channel and voicing I want for my Helix patch.  Nothing changes in the DT.  You can use something like DT Edit to configure your DT that way.  Once you do that all the knobs on the DT are inactivated except the Master and the Reverb.  The DT is basically just a tube power amp now for my Helix.  Works great.  If you don't like it you can always do a factory reset on the DT back to normal.
 
Your other option is to skip the L6 Link and just go in to the DT FX return bypassing the preamp altogether.  If you don't want topology matching that might be the best choice for you.  I don't think the DT Master works that way though so the DT is full blast.  You would need to control volume from the Helix. 

There is some good tips here plus a link to a patch i made in CustomTone.
 
https://www.facebook.com/groups/line6helixusergroup/permalink/537609666422711/

its no harder than any other tube amp.  BUT you must replace with the same brand and type of tubes (EH EL84 matched set).  Do not substitute JJ's or any other brand.
 
If you don't know what you are doing find a professional repair shop.  There are voltages in there that can kill you even when it is unplugged!  Any amp repair shop can change tubes and bias for you.  Here are the instructions for biasing both DT50 and DT25.
 
http://share.myflare.com/rtwSHH

I wired mine very simply with a two jack plate and separate isolated wiring to each speaker.  Then I just plug each channel to its own speaker.  Totally up to you how you rewire if you choose to do so, just be sure you know what you are doing so as not to damage your gear.
 
You should start with the amp at maybe a quarter and bring up the POD volume until you are just beginning to activate the clipping indicator on the amp when you hit a strong chord.  The clipping should not be lighting up during normal play so if it is, lower the POD until it stops.  Once that level is good then you can begin to raise the amp volume to the level you want.

Its really easy.  Just put whatever you want before the amp/cab and a split right after it.  Put all your delays, mods, reverbs, in the new path and nothing in the first path.  Take the clean path output to your amp and take the wet path output to your stereo cabs.  Adjust levels and mix as necessary to sound good in your setup.
 
 

I believe the dual cab option is stereo.  And the Helix manual on page 19 really doesn't specify cabs so much as amps and preamps collapsing to mono.  You need to look for the stereo icon (dual interlocking rings)
 
Keep the following things in mind when building tones:
 
• All Amp+Cab, Amp, and Preamp blocks are mono, so any stereo signal sent into these will be collapsed to mono. As such, it’s a good idea to add only mono blocks before amps and preamps
• Adding a mono effects block will collapse any preceding stereo blocks on the same path to mono
• If you’re only ever connecting Helix to the front of a single guitar amp or PA/FRFR speaker, there may be no need to use stereo models at all (except, of course, for models that are only offered as stereo!)

should be perfectly safe.  Make sure you choose the correct impedance on the DT and as you said, avoid full blast...

totally different architecture, routing, FX, amps, separate cabs, IR's...  no way anything translates directly.  Expect to build all new patches. ;)

You need to change set lists.  Go to the set list User 1 and you will see all his patches starting with JVCleanFXonpedals 1.  There are only patches in the first 4 banks of the set though...

no luck bro.  mine isn't missing either piece but I still hate the design, it is just loose in the shaft and when I use it, I hear a click as it wobbles.  If you are totally missing the plastic sleeve and can't get any help from Line 6 support, you might try using some heat shrink on the trem bar until it fits snugly.  Get it at any electrical supply house.  You will need to use a couple of layers to get the thickness right.  You might also try some plumber's teflon tape as well.  Actually I just thought of that and will try it myself this week...  The set screw will be harder to match up but maybe a machine shop supply house?

Lots of good scoop for you there from Palico.  What iNuke model are you using and what is your cab? Speakers? The Behringers generally overstate their true wattage by listing peak instead of RMS but the smallest one on their site lists at 2X300 into 4 ohms and you are stating 120 so I am guessing you have 8 ohm cab? not quite sure...  pretty certain that is not 120 watts RMS from that amp. 
 
Generally speaking, solid state power amps are pretty clean right up until clipping.  You should have some indicators on the front that will tell you when you are overdriving or approaching it with that amp.  You will always get the most damaging power issues when you overdrive a SS amp into clipping.  That type of signal to your speaker causes a lot of heat and that is what hurts the speaker.  If you are not getting any limiters lighting up, turn up the power amp, its OK.  Turning up the channel volumes and mixer levels can take the input signal too hot and introduce spikes even with the amp not turned up.  Watch out for the limiters coming on. 
 
Is it a mono cab or are you running it in stereo?  If its stereo, don't bridge it! If its mono, you should be OK bridging that amp with your cab.  Like I said, the RMS watts aren't what Behringer advertises.  The iNuke1000 says 1000 into 4ohms bridged so that is maybe 500 peak into 8ohms. Keep your Pod settings the way you have them now and you should get more clean volume and headroom that way without having to crank it.  Be careful with it though, especially if you have a lot of spike volumes when you play.  Just remember, no matter what you do you can't get 4X12 volume from a 1X12 cab...

See the links below for the adapter cable you would use and some extenders if you need more length.  You would plug into the left and right unbalanced outputs, #25 on page 8 of the Pilot's Guide and set the switch there to Amp to begin with.  If for some reason it's not loud enough, you could try switching it to Line.  This will let you use the POD to it's full capability and should work just fine for home use and playing out in a pinch.  Another option is to just get a headphone adapter plug and use the long extender cable to go from the POD headphone out to the POD CD/MP3 input.
 
Stereo Cables, 10' Extender, 25' Extender, Headphone Adapter
 
The truth is to fully take advantage of the POD you will want to get a true FRFR setup, a decent pair of powered PA speakers if you want the capability to play out or studio monitors if you plan to only play at home.  What you have will work fine for now but you are still playing through a guitar cab and speakers and this is not optimal for a stereo POD.  They just don't have the full range you really need and will color the sound on their own.  Don't worry about it though, play with what you have until you really get a feel for it and can make a good decision on what you want going forward.

Sweetwater has the US versions.  I don't see the 89F but they are all custom made to order anyways so I am sure you can order one if you have the cash...
 
http://www.sweetwater.com/store/search.php?s=jtv&sb=high2low

The main point of the DT series is to provide a tube power section to match the digital preamps, cabs and effects of the POD.  It was designed to be used with the pre models and will physically configure itself to match your choice of preamp.  The stand alone DT uses the pre models with cabs to achieve its tones.
 
So to answer your question, you should use the pre models rather than the full amp models.  That being said, there are no hard and fast rules about it.  After all, in LVM the DT will use the full amp model to add a little beef to the tone anyways.  Play around with it to see what sounds good rather than just trying to color inside the lines.  But if you want to match the standalone DT tones, you need to use a pre model with the default cab selection.
 
As far as the L6 link, its only a digital connection and doesn't care what models, cabs, or effects you use...

Yes to both.  If you have a Variax, then in HD Edit on the mixer tab you can define which model to bring up, alternate tunings,  and how the tone and volume knobs act.  On the controllers tab you can also assign the volume and tone knobs to control up to 50 amp and effect parameters each.  For instance you can set the volume knob to adjust the drive, tone stack, compression levels and delay mix all at the same time. 
 
But you have to have a Variax for any of that to work...

they will definitely fit and I see no reason why they won't work... Sovtek claims it has 20 percent higher output than their 5881WXT. As yu see in the link below these are listed in the 5881 tube type section.  Let me know how you like them!
 
http://www.thetubestore.com/Tubes/6L6-5881-Tube-Types/Sovtek-6L6WXT 
 
Always fun to play with tubes...
 

just use the 1/4 outs into the front of your amps.  If you are only using the effects in the POD, no amps, you should set the output mode to Studio Direct.  You may need to experiment with the Line/Amp switch and the guitar impedance settings to get the optimal signal for your rig.
 
Remember that to get a true stereo signal to your amps you must use stereo effects.  If you must use a mono effect like a noise gate be sure it is at the beginning of your effect chain.  If it is after any stereo effects your output will be in dual mono.

yeah, one of your patches is corrupted.  Maybe downloaded or meant for another unit and converted. You will have to load them one at a time until you find the culprit.

rather than change your gear, what about just adding a USB midi connector direct from the mac to the POD?  This M-Audio unit works well for about $40...
 
http://www.sweetwater.com/store/detail/Uno

Hey, I was just busting chops with my first post...  Anyways, I don't think you will get much luck with the echo box into the front of the Spider, just the nature of the digital beast.  As noted above, those effects should be after the amp model but without an FX loop you can't do that here. 
 
The Wah should be no issue first in line into the amp and the distortion will probably work best into the lower gain amp models without other FX in the pre section.  May not play well with the higher gain models or if there are other FX to compete with.
 
The internal delays were pretty nice on my older Spider.  Not what you wanted to hear but probably as good as it will get with this rig.

OK so the first big issue is the guitar plugs into the POD, not the DT when connected with L6 link.  Everything is done in the POD, the DT just provides the tubes and the power amp/speakers. Other than turning it on and setting the Master, you won't touch the DT again.  All communication between the POD and the DT is through the L6 Link (XLR cable).
 
The 3 screens you can see by pressing the View button are the chain of effects, the setup screen and a big block screen showing bank and patch number.  When you are on the setup screen, use the round Nav button to the right of the screen to scroll left and right through the other setup pages.
 
I know it's a pain but you do need to read the Advanced Guide and the L6 Connectivity Guide to get all this.  If you don't have them, you can get them from the Manuals link on the Support page.
 
It is worth a go to connect the POD by USB and use HD Edit for as much as possible.  I hate that little screen on the POD.

triode and pentode refers to the way the tubes operate.  In simple terms its like a three stage (triode) tube vs a five stage (pentode) tube.  pentode is more powerful than triode.

glad you clarified.  Most folks use the 4 cable method to take advantage of their tube preamp section.  You have a solid state preamp with no tube advantages.  Instead what you have is nice solid state power amp and cab, no need for 4CM.  Personally, I would just go straight into the FX return and use my POD for everything.  There are a lot of guys using it straight into the FX return and very happy with the results. And it is MUCH easier to set up...
 
I would definitely use Studio Direct and experiment with amps, preamps, cabs, mics and EQ to find what works for you.  The idea of discarding cab and mic emulation is just wrong.  If at the end of the day you prefer it off, OK, but at least try it to see how it sounds.  You can try the other output types too to see how they sound but I think you will be best with Studio Direct.