How can you evaluate a system with highly processed music?

I don't know why you'd want to evaluate a system with music other than the kind that you like. Personally, I wouldn't care how music I don't listen to sounds on my system. I listen to rock and electronic, so how classical guitar sounds on my system would be meaningless to me. 

I've probably already mentioned this elsewhere, but a violin/fiddle sounds distinctly different when it's under your ear...in other words, you are playing it yourself...than it does when somebody else is playing it, even a couple feet away.

Defining what you mean by "highly processed" would be helpful when asking this question. Do you consider Queen's Bohemian Rhapsody to be highly processed? How about every Steely Dan or Rush album? One could make the argument that anything recorded on master tapes is highly processed. But let me stop with the rhetorical questions. I can listen to a Brian Eno or Richard H. Kirk or Dead Can Dance or Kraftwerk album and find as much nuance and musicality being revealed than if I listen to Abraxas

I can listen to contemporary and earlier electronic and ambient music and can find that the layered complexity can challenge the limitations of systems and also tell you if the system is revealing everything in the recording.  That has to do as much with one's ability to hear vs. listening. 

I find my system reveals more when everyone is asleep and the house is dead quiet and I'm listening on headphones vs. when the house is "alive" and I'm listening w/ my monitor speakers. 

I think the proper question would be how can you evaluate a system with a crappy recording and environmental noise influencing the listening experience. 

If you are looking to evaluate a system you can do it quicker with test tones.  Dynamics, room interactions, frequency response/balance, stereo imagining and depth reproduction can be determined without listening to actual music.  Of course, follow up with a few music selections to confirm your initial findings.  The music can be anything you know well.

Taking a step back, how can we know the level of processing applied to music?   I often wonder when listening to a passage or song the amount of post processing and the source of the sound:  Voice, manipulated voice, computer, synth, instrument . . .