I've read multiple threads where people recommend pairing certain receivers and speakers because the items in question are "bright" or "warm," etc. My question is, can't the receiver compensate for any excess brightness or warmth? I mean, can't the listener simply adjust the sound at the receiver level (e.g., increase/decrease bass, treble, etc.)? Or am I just not understanding the concept?
Others will most likely explain this better than I, but bass and treble controls are just that: increase/decrease for bass and treble.
Bright, warm, neutral type of sound varies among different brands of both receivers and speakers.
For example: mid to lower end Yamaha receivers tend to be on the bright side. Pair them with bright sounding speakers and you'll want to put cotton wool in your ears. Bass and treble adjustments won't take away that overall bright (some might say harsh) sound - it will only lessen or make a little worse the 'bright effect'.
Pair a warm (laid back) receiver with warm sounding speakers and you'll get the opposite effect. The sound will be too warm and bass/treble will only add or lessen that type of sound.
But then in the end, it's all in the ears of the beholder. Experiment until you find the sound that suits you.
Basically warm is emphasis of lower-mids and upper-lows. Cold is emphasis of upper-mids.
I think laid back is not exactly the same as warm.
Mostly bass and treble adjusters have a very large scale, you can adjust the whole level of lows and highs, but detailed adaptation is not possible. Bass and treble adjusters will help you fit your speakers in different rooms, big, small, fur walls, caves & castles...
I dont know about accurate EQs, with them it should be easy remove all emphasis from the sound, but it's not that simple. There are also other differences than those you can see on their frequency responces.
Now I'm so far out of competence that I should probably stop.