True story...?
So before your friend went all in on horns and SETs he was listening to something less than live...and didn’t want it to sound like live before his epiphany?
Interesting that you mentioned the pro violinist, because I know several pro musicians, including myself (well ex-pro in my case) that run to the door as soon as a horn speaker is let loose! Add to that the fact that most of us aren’t that impressed with SET amps, at least all of the ones that we have heard...Not that they are bad, but certainly not the be all and end all that you describe.
Having heard some excellent Push pull amps that utilize the new KT150 tubes, including the new, and excellent imho, ARC ref 160’s, I think SET’s have some catching up to do.