What makes different amps produce different sound?

Since every amp sounds different that's probably the reason people reject that idea. There are many people who think nothing sounds different and that there is no reason to buy anything but a Bose Acoustic Wave Machine.

The same equipment in a different room sounds different.

I bought a highly regarded pair of speakers once based on a review. I sold my other speaker to facilitate this change. When the speakers arrived I hooked them up, let them break-in and then sat down to listen. I almost cried since I was a struggling music lover on a very tight budget and these speakers sounded terrible at best. At a loss to know what else to do, I rewired them with some audioquest wire I had left over from some evil experiment I had conducted on an unsuspecting victim.

I hoped for an improvement, but what I got was much more. These speakers actually sounded good. I kept them for some time before moving up to something else.

The point of all this is to say that something as seemingly inoccuous as wire can make a huge difference. When two amps with similar design use different componants they will sound very different.

Consider too, the companies that modify CD players with new caps and resistors. People swear by these mods, or was it that they swear about the mods... I can't remember.

Unsound, I read an article in Stereophile about ten years ago about an experiment with speakers. The listeners were told that different colored grill cloth was used so they would be able to tell the difference between the multiple speakers being tested.

They ran the listening tests for the speakers and the listeners determined which had certain sonic characteristics. There seemed to be somewhat of a consensus as I recall. The ones with the blue grill cloth had the better bass... and so on.

The funny thing about the test was, all the speakers were the same except for the color of the grill cloth. I doubt that these people would qualify as audiophiles. I don't remember who did the test, I think it was a university in the US, but unsound's comments reminded me of the test.