How can you evaluate a system with highly processed music?

“Audio systems deliver qualitative experiences. Electronic or processed music sounds different as delivered by different systems. Live music also sounds different from different systems. The salient question is: how does it sound to you?”

This👆 by @hilde45

+100!!

The only “evaluation” is whether it sounds good to you or not.  
If it sounds good, the evaluation is: “A”.  
If it doesn’t, then hopefully you can make some sound, sensible choices to improve what’s lacking (you’re in a good spot here on this forum for guidance in this matter) without going crazy on the bank account and sanity quotient.

The way the word “processed” is being bandied about strikes me as problematic.  
There’s no such thing as sound that is not “processed.” 
Person A, with their particular physical condition, particular mind, and particular personal proclivities, listening to a live acoustic instrument, 10 feet away from the player, is “processing” that aural stimulus differently than Person B, even if at the exact same distance.  
Human beings.  
It just gets far more “processed” after that. 
Entirely acoustic instruments recorded by microphones that “process” the sound waves into an electrical signal. Signals then “processed” into a recording. 
Throw in mixing and mastering…. 

Going upwards from here, there are so many different instruments that are electric, there are so many ways to manipulate the signal (intentionally or unintentionally) before it even reaches the recording, there are so many synthesized sounds at the actual instrument stage…

If people have a problem with instruments that aren’t completely acoustic, that’s their prerogative and there’s nothing wrong with that at all. To each their own.

Should such a person make the unwise decision to eschew being a normal, healthy person who passionately loves music and just wants to spend their life enjoying it, to instead become an obsessive, anxiety-addled neurotic who spends more time fretting over minutiae than the former (aka an ‘audiophile’ - I’m being sarcastic, yes, but lovingly so…been there, done that), then that person would just make that acoustic-only music they prefer sound as good as possible.  
Who cares what other people say?  
If someone else makes Skrillex sound “perfect” (to them, of course) in their system, that person has “evaluated” their system, and given it a grade of “A.”

@simonmoon Define, “accuracy.”

”Sounds exactly like a violin does in person”?  
“Sounds exactly like a piano does in person”?

This may be true to the listener.  
Sure, it’s possible someone may “get it right,” or “as close to ‘right’ as possible.”  
A person may be able to perform some scientific process of, say, a trial run involving the placement of a world-best conductor and/or orchestral player in the “sweet spot” of their listening room for an hour’s time each trial, ultimately coming away with a significant-enough sample size of “yay” votes as to the system’s “accuracy” to be able to say, “this system is super accurate.”

Other than this extremely rare extenuating circumstance (to the average Joe at home), a listener is determining “accuracy” from a place of inherently-questionable science.

Then we look at the definition of “accuracy” again: being able to reproduce what was performed at the performance stage as accurately as possible, being able to reproduce what was heard on the studio monitors at the time of recording/mixing as accurately as possible.  
To say, “now that I’ve determined reproduction of acoustic sound is ‘accurate’ on this system, I know that reproduction of pop recordings will be ‘accurate’ as well” is problematic.  
Hearing what the pop artists, engineers and producers were hearing when they listened to the studio monitors/master tape at the time of recording/mixing is not necessarily achieved across the board after determining “my system is ‘accurate’ based on classical music reproduction.”  
A different set of principles is adopted when making a pop record.  
A setup that is “super accurate” for reproduction of recordings of exclusively acoustic instruments may not necessarily be “super accurate” in reproducing what was heard on the studio monitors/master tape on a pop record.

Saying, “this is as close as possible to what the artists/engineers/producers heard on the master tape of this particular pop record” can only be achieved by having the music/recording’s progenitors sitting in your “sweet spot” in your listening room saying, “yup, this sounds exactly like the master tape.”

The classical recording/mix/master and the pop recording/mix/master are two pretty different things.

Beyond this point, the variables become so overwhelming across the entire spectrum of music-listening as to make a proclamation of objective “accuracy” across the board pretty silly.