I have most of my FX (Phase 90, Chorus, M5, Carbon Copy Delay) all before the preamp. The only thing in my amp's loop is a second M5 for 90% of my delays. It is all controlled by a Ground Control Pro and RJM Rg-16 switcher via MIDI. The loop is set to series and I have tried adjusting the level via the loop controls. No luck. Anytime Loop 5 (the M5 for delay) is engaged there is a slight yet noticeable volume boost. It happens with any delay model. The only real solution I have found so far would be to add a Line Boost to the amp's loop and have it engage anytime I am in a non delay setting to even out the level. I did not think it was very noticeable until I was playing out and had a great monitor mix with my guitars in it. I hit a big A chord and halfway thru it ringing out I engaged the M5 and I could hear the very noticeable jump in volume. It's not like a huge, smack you in the face boost, but it is enough that our sound guy mentioned it. I do know that the manual for the Bogner says "If the effect has "level" switches, set them to "+4". Not sure what the level is coming out of the M5. Hope that helps.

There is a schematic attached. The M9 is now the M5 in the amp loop.

Unfortunately it isn't the loop. The amp loop is on all the time. Only when the M5 is engaged within the loop does the boost in volume occur, so it is most definitely the pedal.