There are some basic, but VERY important questions to ask when purchasing an amplifier:

• Will your amplifier properly drive your loudspeakers? For example, Electrostatic speakers thrive on VOLTAGES not CURRENT or WATTAGE.....Some speakers are EFFICIENT, but require lots of CURRENT to keep their woofer under control properly. Remember, too that watts are nice, but for cone speakers CURRENT is important. See next item.....
• How well will the amp CONTROL the speakers? Remember that when your woofers are moving in and out, it's because the signal's passing FROM AND TO the amplifier! If the amp can't handle signals going both ways effectively, controlling what it's giving the speaker AND WHAT THE SPEAKER IS GIVING BACK TO THE AMPLIFIER, your sound will SUCK. Bass will get muddy or "wooly" instead of being clean and articulate.
• REMEMBER THAT THE AMP IS ONLY ONE PART OF A CHAIN OF COMPONENTS. KEEP THINGS IN BALANCE SONICALLY AS WELL AS FINANCIALLY.

• How much HEADROOM does it have. Is its power rated "best case" or "worst case?" It may be rated at 100w/ch, but at 101w, it's shot. A good amp should be able to go far beyond its rated power for a short period of time (seconds not milliseconds) to reproduce big peaks in the music signal

• Can your amp properly reproduce a 20 Hz square wave? Years ago we actually hooked up in our shop a square wave generator, and our little HK AVR30's 60w/ch amp had no trouble reproducing a 20 Hz square wave. The speakers' woofers would click sharply in and out as "told to" by the amplifier. A Carver amplifier costing many times more, and rated at 200w/ch couldn't BEGIN to pass the test...lots of watts don't equal CURRENT and CONTROL. TRUST YOUR EARS....
• THD - total harmonic distortion - isn't always a good indicator, unless you know WHERE the distortions are happening. For example, solid state amps produce much lower THD than tube amps, but the tube amp produces a type of harmonic distortion that the brain has NO PROBLEM with, where solid state amps produce a type of harmonic distortion that the brain HAS BIG PROBLEMS WITH. Specs are just numbers until you understand more about what they mean.....A good "spec" doesn't mean your amp will sound good.l