How can you evaluate a system with highly processed music?

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.

Dear @mglik : All recorded MUSIC are way processed through the recording process steps been acoustic or elctric/electronical: it needs microphones to start with the process.

" How do you know what that sounds like? "

We really don’t know for sure even with acoustics because one thing is what we listen in a live event and what we listen in a room/system at home. Yes we can evaluate what for our live MUSIC experiences we think is near to those experiences.

We all started our room/system evaluation for 10-20-30 or more years when step by step wse gone changing speakers/electronics/CD players/cartridges and the like and through all that heavy learned room/system " voyage " learned to evaluate a system almost any system.

In my case through all those years a test/evaluation process was created where I was choosing some recording tracks in LP/CD that through the years too were changing and improved and I could say that today my evaluation process with those choosed recorded tracks is almost bullet proof.

I use almost everykind of MUSIC from the Telarc 1812 LP passing for the D2D M&K Flamenco Fever and the Sheffield Drum record and the Paramita LP by WindMusic label or the CD Gladiator even Laura Branigan Self Control single and Fun Fun Color My Love 45rpm Maxi Single and the great voice of Montserrat Caballé , Kabi Laretei on piano Chopin Nocturne on Proprius label and Center Stage by Wilson Audio Label and other more as the RR Dafos. I know on each one track even the tone of diferrent recording mistakes or clicks/pops.

Different tracks to evaluate different characteristics on MUSIC and ovbusly always the same tracks for evaluation of those different characteristics.

Well that’s me.

Regards and enjoy the MUSIC NOT DISTORTIONS,

R.

@larsman 

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

Long before I was into classical music, I still understood, that it is recorded with much less processing, and in ways that captured the natural spatial cues of the acoustic space it was recorded in. 

So, if a system reproduces classical music accurately, I have a better chance of knowing that what I hear on rock recordings, is accurate to the way it sounded when the band and engineers were done with it. 

It is a great way to get a baseline. 

Without that baseline, rock recordings may sound good, but not actually be accurate.