This is sure to get interesting. Briefly, I can offer that everything affects the final sound of the amp. It is very important to remember that the amplification stages of the amp do nothing more than modulate the output of the power supply. The quality of the power supply and isolation of individual taps from that supply, be they input, phase inverter, output, bias, negative rails, etc., is even more important than the quality of components such as caps, etc. in determining the final sound.
Bottom line, don't skimp on the power supply.
I know this isn't exactly what you inquired about, but hope it helps in conjunction with the other information about to come your way.
Two excellent starting points: Morgan Jones' "Valve Amplifiers" and John Broskie's blog: TubeCad Journal.
http://www.tubecad.com You can start with the journal, John is brilliant and innovative. He offers excellent descriptions of the functions of various amplifier stages. Start with his earliest blogs from the late 90's. They addressed some of the simpler stages before getting into the really complex.
Hope this helps.
Stuart