All those things make a difference, it is also how the designer chooses to implement them. Your right that we are not talking about tube amps but we are talking about AVR's which include the pre and amp stages all in one to create a sound and there not all the same.Different sound is accomplished from different processing of the signal, such as from: tone controls, surround modes, room correction, etc. Amplifier channels themselves hardly change how something sounds, if at all. We are talking modern AVRs here, not old tube amps.
IME I have demoed 2 to 3 different receivers in my system at various times, all calibrated to the same levels. Some were so close you could not hear a difference but others either possessed a more laid back sound or a forward sound that could be grating to listen to. I would normally keep a receiver I was demoing in my system for at least a week or 2 before switching out to the other so I could get a good feel for how it sounds.
Sorry if you feel that receivers that have a "warmer" or sound better for certain types of music is just heresay but IME that was the case.
We just have a difference of opinion, I respect yours, I hope you respect mine.