You get the best of all issues by using both the "guitar" and "aux" inputs via a split feed. The level is not doubled w additional noise floor like "same". It sounds better, simply A/B it. Using "same" increases the input level which may or may not be helpful when you do not want it. And the noise floor is worse on "same", again simply A/B it. Try not to make all tone judgements and tweaks using just uber gain tones which simply cover over most issues. Fine example is the noise gates, uber gain you do not hear how they are effecting the tone and bandwidth of the true signal.
The case of the 6 db drop on the loop is not noticed on the 4CM method because the gain level is hiding the drop. Any avid player should realize intense gain hides a lot of issues like levels.
If you run pedals in the loop you will find when engauged the level drops so much you cannot properly drive effects at a std level. You can try line level but w effects level pedals this is not cool, might help the amp but not pedals. Simply A/B on/off on a clean sound and there it is a level drop.
Prevented me from trying to use the POD on the 4CM, no matter the fixes rendered by several also seeing the problem, everything just served to increase the noise floor so badly it was not useable. I believe L6 has the loop level lowered because it has a high noise floor and they are trying to keep that unnoticed for those commonly using the 4CM. One might consider the effects loop has a return level increase "from zero boost" but the output is exactly opposite, comes up to a "zero db" increase but that send level is several db lower than unity. Obviously if I am seeing it, it exists. I am not a teenager not knowing how to rig boards.
This became a deal killer for me on using the POD. While I consider the unit an excellent bang for the buck and perhaps an excellent fun recording tool. Several issues with the unit just built to the point I stopped using it as the basis for my tone.
Critical issues (of which Line 6 offers nothing or no hint if they intend to fix these issues or can)
1) Pitch Glide edit controller is set on percentage of pedal sweep w no decimal fine. It is impossible to set the pedal for a true in-tune interval like a 4th or a 5th up or down, like a REAL Whammy easily does.
2) Effects loop level suffers an apparent 5-6db drop. Various means to increase this internally and externally increase the noise floor hiss and do not sound natural. I put a transparent class A clean boost on the effects output and it brought the level up to unity but the noise was unuseable.
3) Digital noise floor hiss, can be pretty bad in this unit mainly caused by over pushing effect outputs and levels, which do not work the same as the physics of a pedal board signal to noise ratio. I never had to use a noise gate or NR pedal before I got the POD. While with cleaner amps and such it can be avoided, at some point one has to set one up to stop the noise floor of this unit no matter how well you control levels and work to get the preset quiet. Problem is noise gates are not transparent to the tone, not at all and again using intense uber gain covers up these issues but they are there in frequency response and bandwidth.
4.) the majority of effect models are just not that great and although one compensates and uses various tricks and mods inherent to the POD, anyone is kiddind themselves that these effects are as good or close to pedals, they are not. Pedals used in front of the POD work very well, no problems, OD, boost, compressors work well against the POD amp front ends. But the "effects loop" with pedals, seriously, does not work.
5) If you are using the POD for an effects bank it pales next to quality pedals, a mimic of a cheesey pedal is no less cheese. The PODs best ability is its amp models. If you avoid these there is little point to having the POD, sure an array of effects of some quality can run 4-5 times the cost of a POD or more so at best it is a no budget means to get some effects. Some are quite good, I like the wahs, turn down the level a little and they are fine, ODs no, Dist's hell no, Compressor models are pedals I never like much to begin with. Modulations, some are good, Delays fine, Reverbs good. That being said you CAN develop decent tones from this unit and if that is all youc an afford you use what you have. Myself I would rather see less effects and a few better models. Seems to be an option on the POD that trying to use 2 amps sucks up most of the DSP and leaves next to nothing for any effects, not a great trade off. Buying the unit for its AMP modeling, good idea, buying to for an effects bank and library, not so much.
----Big down for me is customer reponse and notification of issues, Would it kill them to respond and say hey we know about that and are working to update it or we cannot fix that issue. Instead of we cannot duplicate your problem or a host of fixes which have nothing to do with your problem. They never drop a hint as to what they are working on or planing or response to anything you suggest as a tweak or a needed fix. That is not cool and is terrible customer service. I am not some teenager to talk down to or act as if I must be imagining a problem. When you hit a wall using a device you typically move on, you do not wait like a litle kid for christmas hoping santa got your letter and what you wanted. -----
1)Amp models are excellent of course higly dependent upon what you run the POD into or with. I got some amazing realistic superb tones avoiding the POD effects loop and using a std guitar amp by simply feeding the full range stereo 2 chain capable (HD500) signal into a full range power amp feeding a stereo split wired GUITAR cab. The real guitar speakers and transparent amp allowed the POD to sound like the real amps in some cases rather uncanny.
2) Pedals in front of the POD work well as long as you do not try to slam the input level w too much as the digital platform does not like excessive levels externally or internally.
3) Do not get me wrong, spend the time, learn the unit, read everything you can find about preset programming and tips and you can develop some great tones. The over used myth of thinking plugging in a preset of "sounds like" is going to make this unit easy and simple to use and "sound like your hero or tune" mentality is just a young players mistaken notion that copying someone's gear makes you sound like them. And seriously if that is all you do is copy and mimic while being fun in the short term that is not true music or creative muse. Learn to create and improvise or you remain a low fi mimic.
For those who refuse to read manuals or learn how a unit works or what it can do, the HD POD is not for you. It is not a plug and in and play and sounds like magic box, it is a tweakers mad scientist lab and can be a real hoot in recording or experimenting. Better than a well designed pedalboard, nope. The POd is limited to what you do with it and more importantly how you run it.
4) The ability of this unit to hold and externally store an infinite number of presets and tone lists is amazing. The ability to download software updates and tweaks is outstanding. Now if L6 would changed their policy of ignoring requested or needed fixes and offering no hints or mentions of what they plan, or can fix, is not something older experienced players have time to wait or the patience.
I have a special rig for the HD500 with a power amp which sounds amazing. But integrating it into my tube amp half stack was a disaster due to some of the limtations of the unit and no indictation anything is being fixed. So w my great sounding amp it is placed only in the amp loop and used for some modulatio, delays and reverbs, and just with that one can load a lot of options with the PODs switching ability and many memory slots. Have a great amp, you probably do not need a POD, have a crappy amp or a low powered designed clipping amp, no way the POD is going to make it sound like a ENGL or Marshall. Want to hear the stare of art in amp models feed it into something that allows it to do that.
That being said, I leave each of you to your opinions and what not. As you encounter some of the things I mentioned you will realize it was all true and factual.