Think about it, the purpose of amplifier is to amplify a signal, not to change it in any other way. The closer the output is to an exact magnification of the input, the more provably "correct" the amplifier's function is. Color and change the sound all you want, run it through a series of guitar effects pedals if you wish, but the amplifier really doesn't have a place in coloring the sound because that's an uncontrolled variable in the chain.
I can insert a tube (or digital simulation of a tube) into my signal path if that's what I want to hear. I can also turn it off.
Amps can and will sound different because there is a such thing as signal paths and amp performance. I can buy a cheap 100 watts x 2 Pyle amp but to expect it to perform the same as my Pioneer Elite is folly, the specs simply do not match up. Just as I cannot expect the Pyle to outperform the Sansui, the dynamics simply would not be the same and no way will the Pyle sound anywhere near as good as it. An amp is just one of the 1000's of variables that exist from one receiver to another. In certain controlled environments, I am sure amps would sound similar. If using poor speakers, maybe you cannot hear the difference as much but not hearing it does not make it disappear. In the real world, DSPS, OPAMPS in the DAC, the input used, room correction, the room, the speakers, etc. All these things change sound quality. It's called reality (real listening) vs unrealistic environment (ABX).
While it is true an amplifier's job is to take a signal and amplify it, there any many different and now more exotic amp types. Solid state, tube, chip, digital, A, A/B, D3, hybrid, discreet, etc. No two amps have the same specs, this is why the more expensive receivers sound better than their lower end counterparts. This is why you would buy an Anthem over a midrange receiver because you are paying for the sound quality and amp quality. You are getting less features with that more expensive Anthem, therefore if they are sound the same an Anthem or Nad or Cambridge would be useless to own when you can get a cheaper receiver for 1/3 the price and get more features to boot.
Arny and Kbarnes701 remind me of cultists, they think ABX tests are "common sense" when I find them unrealistic and biased towards people like themselves. ABX is an unrealistic environment. If an ABX test was carried out by using receivers at their full potential, I bet the differences would be very apparent. Do not mistake, I do think ABX tests are interesting and the results interesting, but it is just funny that exactly half were able to pick out the difference, but according to boiled spinach boy that is just "random guessing".
Edited by Ricsim78 - 2/8/13 at 11:47am