You don't need to convince me. I believe you. However there are many strong influences that can lead to that conclusion and they are :
1) Sighted bias - knowing you are listening to an AVR/stereo amp can lead to all sorts of conclusions that agree with your expectations and preconceived notions and may have
nothing to do with sound quality.
2) Mismatched volume levels - unless formally done, you'll hear a difference based on poor level matching about 100% of the time. Unless this step is taken, impartial judgments of sound
cannot be made.
We won't even cover auditory memory and how there are time-limits for that as well. Fact is, audiophiles in general make a big deal out of stereo amps sounding so much better for music, but if they really could "hear" this "OMG" improvement they would have no problem demonstrating this in a controlled test, which ... we know they cannot do.
Fact is, many audiophiles like to brag about their hearing abilities and like to brag about their audio gear but very few have the chops to put their hearing abilities to the test. When they hear "blind test" they run ... far, far away.
Fact is, if you were forced to judge sound quality on the basis of using your 2 ears (no peeking allowed) with levels carefully matched, it is highly unlikely you would think 2 channel amps sound fantastically better for music.