I only agree with Peter so far. I've heard differences with amps and preamps, even when the test was blind. But, he does make one good point in a recent editorial.
All of the things that the typical audiophile worries about: preamps, amps, DACs, CD players, SACD, wires, tubes, and on and on... pale to insignificance when compared to speakers.
The difference between a $100 amplifier and a $100,000 amplifier is small when you compare it to the difference between two speaker systems. Hell, sometimes the difference between two pairs of the same model if quality control isn't the greatest!

Peter managed to completely ignore the listening room in his editorial, so I guess his listening room is perfect.

Still, we're talking about the same end of things. The electrical to mechanical to acoustic process. The large flaws are here and they almost certainly swamp the difference between electronic components like amplifiers.
Spend your money on everything after the speaker cables.

Do I really believe that amplifiers sound the same? No, I think there are differences and I've heard them.
But I have noticed that nobody has problems telling the difference between 2 speakers systems in a DBT. They may have a problem telling the difference between two amps, but not speakers.
Speakers have more wrong with them than electronics at this point in time. So I think the average audiophile should spend more time and effort where it's called for - beyond the speaker cables.
Oh yes, the vinyl end of things has plenty of problems too, but we can avoid those by using CD.
