agreed about amp distortion. a slight boost can be ok, if it's being put over amp distortion, but a pedal over a clean channel (unless it's a pretty light overdrive, which can also be ok), not really a fan.
I agree with that. But what is bugging me is that if you use the Amp's distortion (which I do on all my amps) you have to use the loop to get delays sounding right in overdrive (which I always do). If it's only light crunch on the amp and you kick it with a pedal, you can put the delay between drive and amp and it's fine (what most people do on 1Ch amps, like a Plexi).
Whenever I used loops, even the better ones (new gen. Shiva, the XTC which is switchable, the Einstein) then I can stillrecognise tone degradation. Must be a level thing mainly, as I think amp builders have to do a lot of attenuating down and amplifying up again before Send and after Return. This impacts the integrity of the signal flow (which is the biggest advantage of tube heads vs. tube racks.
There are hardly any amps that I've tried, where the signal stays as punchy, meaty and juicy on the drive channel with the loop in use. Maybe the Einstein was Ok, but the overall tone of that amp wasn't too much my thing anyways, a bit too much sound and not enough tone, if this is an expression that makes sense - just wasn't as lively or organic as some other amps I owned.
So that's why I think using a Plexi style amp on the verge of breakup together with a Wah, a Boost, an Overdrive and a Delay (+ maybe a Chorus/Trem or sth) could be the way to go. But it would need a PPIMV for me.