Actually, I have done 2 sighted tests in the last 12 months or so:

1)


At one time, I had Proceed (fully balanced with balanced connectors), Bryston (not balanced with balanced connectors), and Acurus (not balanced with just RCA jacks) amps all on hand at one time. I did extensinve listening tests over about 6 months. 2 channel music and movies. I ended up keeping the Proceeds. They just sounded smoother on top with more mid range detail and clarity, to me.

2) Drove 160 miles last summer to go listen to a Pass Labs X150.5. At the dealer, I also compared that amp to an Aragon 8008 Mk II. (The Pass Labs is fully balanced, the Aragon isn't.) I preferred the Pass Labs amp. This is the most musical sounding amplifier that I've ever heard.

Now, I personally don't think there are large differences between amps. I agonized over the decision to replace the Acurus amps, that in one form or another, I had had in my system for about 8 years with the Proceeds. The Proceeds cost a fair amount more, and even though I did prefer them, the differences were subtle at best. But to me, they were there. The point is, is that I had no ulterior motive to preferring the fully balanced design in this case, and in both comparisons, the fully balanced amp certainly did not sound *worse* than the single ended designs.

So there.