How can you evaluate a system with highly processed music?

Test tones? Seriously? That is ridiculous. Music is simultaneous sounds at vastly different frequencies fading in and out at grossly different rates. The system has to be able to reproduce them all without interfering with each other. Nearly infinitely more difficult than test tones.

“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.”

Pace John Atkinson and his bass, but it depends on how much processing.  If he just amplifies the sound direct from the instrument using a vanilla amplifier then yes, a direct comparison between systems can have validity.  But if the signal is processed to the point of being artificialised then there is no basis for comparison.  All you can say is rendition on which system excites you the most.

@mglik 

Each to their own.

But can you really evaluate a system by listening to highly processed, electric/electronic music? How do you know what that sounds like?

I like to listen to voices and acoustic music that is little processed. 

Instruments like piano, violin, etc. 

And the human voice. And the joy of hearing back up singers clearly, etc.

Even if full instrumentation backing a natural sounding voice.

(eg.: singer/songwriters like Lyle Lovett or Leonard Cohen)

There is a standard and a point of reference that can be gauged.

OMG!

I've been saying this for years. And have posted it on various audio forums. 

At least in order to get a reasonable baseline of how accurate the system is, or in order to tell if a change made an improvement or not. 

Most people have heard acoustic instruments, and have a good idea of what they sound like. And if they hear those instruments, with minimal processing, on a system, they can tell how close it sounds to hearing it live. 

But with musicians playing electronic instruments in the studio, even if we know the guitarist was playing a Strat, we can't possibly know what effects they were playing through, or how the engineer manipulated the signal after it was recorded. Things get even worse with synths.

Then there is the entire aspect of soundstage and imaging. The vast majority of studio recordings, if they have any semblance of soundstage and imaging, it is almost completely artificial, created by the engineer using: panning, delay, phase, and other studio tricks. Not to mention, the musicians are usually not playing at the same time, in the same acoustic space, so there is no natural relationship of  musicians to the space, or the other musicians.

Where, with classical recordings, for example, all the musicians are playing at the same time, in the same acoustic space, where recording engineers take great effort to capture the event as it happens, with as much of the ambience and other spatial cues of the acoustic space (usually using something like a Decca tree or Blunlein mic setup) .

Therefore, if a violinist sounds like they are coming from the left of the other musicians, or the percussionist sounds like they are coming from back of the ensemble, it is because that is where they were when the recording was made. Not because the engineer panned them to sound as if that is where they were.