What makes one good amp sound better than another?


I currently own a pair of half-decent speakers, Martin Logan SL3, driven by a Adcom 5503 3-channel amp (one channel for my center speaker). This amplifier is rated 200WPC in 8 ohm, and 350WPC in 4 ohm, and has no problem driving the MLs. I have been told since the day I bought the MLs that these speakers will expose any deficiencies within my system my amplifier included, because its "transparent" sound. Now, I am thinking about potentially upgrade the amp to something more "hi-fi", maybe Classe or Bryston, or Parasound's new Halo amps. However, I still don't know how one amplifier can sound so much different or "better" than another, assuming both are solid state and relatively well-executed, with large power supplies and capacitors etc. For example, I used to think Krell is the pinnicle of amplifier designs, but then I read from various forums that Krell amps are good for bass but have rolled off highs. How is it possible (I mean rolled off highs?). If one lookes at their spec, I am sure the frequency response is not much different from other high-end amps. What determins the sound of a high-current, mid-to-high wattage amplifier? When people use words like "fast", "transparent" to describe an amplifier, what does that mean? How can one amplifier generate wider sound stage than another? Even if I have money for a $3000 or higher SS amp, am I really going to gain much more than my Adcom?
loujo
Amps have as many differences between competitors as do any other components.

However, I believe there is one difference pertaining to amplifiers over other components:

When you find the right amp, it alone is by far the greatest contributor to a system's sonic pleasure. But finding the right amp can also be like finding a needle in a haystack.

-IMO
A good way to try to draw distinction is to audition different amp models under the same brand using same front end gear and softward. e.g. for Musical Fidelity, try the A3.2, then the A308, then the kwp. Different price points, various circuitary, power, etc. You WILL hear the difference.
As stated from previos posts YOU MUST GIVE TUBE AMPS A TRY.
The Matin Logans will come to life with a ARC VT-60 if hooked up correctly or a ARC VT-100.Good Luck