I'm running the pioneer pre-out to a Pre-amp with fixed vol at 0db (851E) that goes to power amp.
What i mean is lower the fixed input to -12db.
I'll run later the mcacc setup again with a tripod.
Why stick another preamp between the AVR and the amplifer? In any event, yes, I would turn the preamp's gain down to get the AVR's trims within about +/-3 dB of 0 dB, or at least within +/-6 dB. you can adjust the gain then run just the level-setting part of MCACC in manual mode to dial it in. Reducing by 10 dB or so is probably a good starting point. You may need more than that since the preamp adds some gain.
"After silence, that which best expresses the inexpressible, is music" - Aldous Huxley