You mention, rich, warm, and bright. It is one thing for people to say a speaker is bright, warm, chocolaty, etc. Speakers are probably the least accurate part of the sound reproduction chain, and can be designed with a particular voicing. Again preamps/receivers can EQ or have tone controls that will have some effect on the sound. The amp should be the thing that adds nothing to the signal. It has one purpose, to take in input and output it louder. An amp may make the bass tighter or transients snapper, but if you are expecting tone shaping you're looking in the wrong place.
The only thing which should have less affect on the sound is the cables.
