Live music is the best reference to judge how good an audio system really is. I like Bruce Springsteen, Dire Straits, Doobie Brothers, Pink Floyd, Jethro Tull, Joan Armatrading, Gloria Estefan, Steely Dan and others. I have heard all of these live, some more than once. As you probably know, not one of them normally performs in concerts that are completely acoustic with no electronic assistance. So what do they REALLY sound like? Is it the sound from the speakers in concert, the sound going live to a 2-track recorder (when available), the sound at the sound engineer's seat? Or maybe the multi-track sound in the recording studio when the LP or CD that I own was made? Is it realistic to eliminate any electronic music (electric guitar, etc.) as a reference recording unless we were present in the studio when it was recorded?
I have heard many Beethoven symphonies live, but unless I was there in the concert hall when the particular recording that I own was made, just going to live concerts, while certainly valuable and enjoyable, will not provide the reference for what I hear through my stereo system when playing a recording of a different performance of the same music than the one I attended. And then there is the whole issue of aural memory, and how accurately we can compare sonic events separated in time. This is a complex subject, but I hope I am communicating the idea that "live music" is not an easy reference point in the context of stereo system evaluation where components change frequently, and where even the time of day can alter what we hear.
Possibly the most valuable aspect of live, acoustic music for the evaluating the truthfulness of an audio system is the feeling one often gets of the music's purity, sweetness, dynamics, and transparency. While it is is often difficult to recall exactly how a cymbal sounds in all its complexity and then, later, listen for that level of detail back in the listening room, we can much more easily understand if a stereo system recreates the feeling we enjoyed from a live performance.