When I "voice" amps and preamps I am always trying to make them sound like they are not there. I have a Lampizator Pacific DAC so the front end is killer. I am always trying to have the amps vanish. That is the goal. They should just sound like music and not be warm or cool or anything. Lynn's circuit is amazing. If you put a really good power supply in front of it and really good output transformers behind it you get the vanishing act......
I "voice" things mostly with recordings of acoustic instruments and vocals of course. Does the piano or mandolin sound real? So I have my favorite 100 test tracks. Of course I enjoy Pink Floyd or a live Dead show, but you don't really know what the electric guitar is supposed to sound like. That sort of music will tell you if your amp rocks, but not if instruments sound convincing. I know what a mandolin or stand up bass sounds like. I love David Grisman's acoustic disc label. I love the last recording of the Goldberg variations that Glenn Gould made. If I can easily follow the left and right hands with no strain, then the amps are good. I really like Myriam Alter's compositions. She plays on some of them, but they are always interesting music with hints of Klezmer and all sorts of other influences. They are usually 3 to 5 instruments, like piano, clarinet, bandoneon, and interesting percussion. If you can easily follow an individual instrument or switch to listening to the whole, then the amp is good. I find this circuit to be FAR better than any amp I have ever heard. The reason is that it avoids many sorts of distortion that plague other circuits. You don't really know you are listening to all of that until it is gone, or at least very minimized. So what you hear is really the lack of all the other things you usually hear in other amps. That allows only the music to remain, floating in the air in your room. I find it quite astonishing after all the years of restoring classic tube amps, and then building my own, to hear what this approach brings. Very enlightening.