Why do amps sound different?

Cost. Every amplifier is designed to a price point. Since there's no such thing as a perfect amplifier, each manufacturer strives for the best sound within a budget (assuming that's the design criteria). Everything inside the amplifier imparts distortion - there's no getting around it - so they compromise as best they can. Forget bench numbers (see: Tube Amps), the sound of an amplifier is mostly based on what the designer hears as he's voicing the amp. And since no two people will neccesarily concur what is the best way of doing things, there's will always be differences - whether it's amplifiers or pizza.

I'm thoroughy convinced that we don't know how to measure some things that really count- and that's why amps sound different at similar specs.

What are those "things"? I have no idea.

My bet is that the perception of reproduced music is extrememly complex, and we humans are still not as smart as we believe ourselves to be.

Amps are like ice cream flavors. I agree with most threads here but, amps embellish certain freq. ranges to tickle our ears. We like what we like! Most really nuetral amps don't sell that well.

We need to bring back Julian Hirsch from the grave to recite all his articles in High Fidelity magazine that covered that subject. Do you remember Julian? He was of the test bench school.

Nah, leave him there. It's threads like this one that demonstrate how few people understand what the test bench tells us and doesn't tell us.

You don't listen to an amp. You listen to a system.