Schmalle

This is true.

Regarding DSP power you can think of it as having two HX Stomps in one box.

Try a compressor with mix parameter - start with 0% mix and then increase. That will add sustain and body while maintaining the acoustic guitar's transients. The Ampeg Opto Comp is my fav for that.

It can be a head scratcher for sure. Disabling Snapshot Bypass means disabling the snapshots' control over the block's bypass.

There is another way, too. You can use only Path A and a FX Loop block as a separator between instrument processing: In -> processing for Instr 1 -> FX Loop (100% mix) -> processing for Instr 2 -> Out Instr 1 plugged into Input 1, processed signal from Send. Instr 2 plugged into Return, processed signal from Out. This requires using an FX Loop block (and therefore unnecessary DSP usage) but it frees you to use Path B for parallel FX in the patch.

No, the Stomp has Path A and B which are both stereo paths. If you use a Stereo Return block as the first block in Path B and route it to Send you can have two fully stereo paths from input to output

Yes this can be done on the Stomp. You use L and R inputs for the two instruments - lets call those instruments Ren and Stimpy. In the patch you use Split Y (panned hard L/R) to separate Ren and Stimpy: Ren on path A, Stimpy on path B. You can now process both instruments individually. You can then merge both paths again (using the Merge block panned hard L/R) and output Ren on out L and Stimpy on out R. Alternatively you use the Send as a stereo out for Stimpy and outs L/R for Ren.

You can use an impedance balanced TRS out with either TS or TRS cables. If the device you're connecting it with has a balanced input (e.g. mixer) then a TS cable works but a TRS cable is preferable as it gives you the noise suppression and optional ground lift (by taking advantage of the third/ring lead). If the device you're connecting it with has a unbalanced input (e.g. amp) then both TS and TRS cables do the same work (TRS cable works but has no advantage because the third/ring lead is connected to ground /deactivated).

From your description it's hard to determine the problem. The detune artifacts might be caused by a time parameter (delay, pre delay or something similar) that is changed via snapshot. You could post the patch (attachment) to let us see what is going on there. You could also do a test and bypass or delete all effects and listen whether the problem remains.

You can prevent individual blocks from being affected by snapshots using Snapshot Bypass (an option when you select a block and press Action).

The outs are impedance balanced. This means the signal is only on the tip pin. It still has the advantages of a balanced signal transmission (noise rejection and the possibility of ground lift). https://www.soundonsound.com/sound-advice/q-how-impedance-balancing-audio-different-normal-balancing

Cali IV Lead can do Metallica clean, crunch and lead. It can also do GnR and EVH. You can play a complete heavy rock Top40 show with that model and a humbucker guitar. I use it with the 4x12 Greenback 30, 906, pos6, 1.25", 45°, 110Hz, 9kHz. It sounds pretty much like a specific scooped IR from the Ownhammer Classic Rock pack.

I understand that. There are solutions to it - see above. If I had that problem I'd search on the used marked for a Nobels MS-4 which works via MIDI. Or build a relay switching box.

Essentially you want to enable/disable the expression pedal assignment for reverb mix with a footswitch, right? No, you can't bypass assign a controller assignment.

By using Bypass Assign instead of Controller Assign. Use the CC message to bypass the Split block and toggle between default value (bypassed) and your setting (activated).

If you use the fx loop make sure Global Settings -> Ins/Outs -> Return Type is set to Return. If that's not it: post the patch as an attachment.

Take a walk in the PARK!

"Line 6 Will".

Older HX FX had a hardware problem causing squealing that is fixed in the current version.

I don't think you're doing anything wrong. It's just that you're plugging into a HOT tube power amp. You could use the Vitriol preamps to match (A/B) the EVH channels and figure out what their actual levels are. Probably quite low.

I agree, the manual should be more clear on the technical stuff. Maybe that's by design to have wiggle room for 'silent' improvements. The 1/4" Outs are balanced. When the Helix outputs are set to line level, they are +4dBU nominal with approximately 15dB of headroom. Source

That's a ground loop issue. You need an isolated switcher, something like the Voodoo Lab Control Switcher. There have been some DIY versions of relay based switcher devices presented in this forum that use Helix's amp switching out for that (instead of MIDI).

Yes, the volume knob is subtractive unless it is cranked.

Does the noise from the amp disappear when FOH is not connected? Does the noise disappear if you bypass Dist and Amp blocks?