Well, I tried it and my Denon does not appear to care about the master volume.
1. I set the master volume to -70dB. I manually engaged the test tone out of my left speaker and the SPL meter read 74 dB.
2. I then came out of "setup", I set the master volume to 0dB, went back into "setup", manually engaged the test tone out of my left speaker and the SPL meter read 74dB.
The way I look at it, the channel trim sets the relative level between the speakers. So it doesn't have to care about the master volume. The master volume simply raises the level on all speakers equally.
