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.”
I think the OP is only referring to evaluating a system, not what one is going to listen to for enjoyment at other times.
And yes, all recorded music is processed. But, without argument, classical is by far the least processed, and much closer to being an accurate representation of the original event than any studio recording. What is on the recording is much closer to the actual sound of the instruments, than the average studio recording.
The vast majority of classical recordings, are usually only slightly compressed, minimal EQ, minimal mixing. There is no: quantization, noisegating, autotune, panning, delay, echo, etc, used on classical recordings.
There are much fewer layers of processing between what is on the recording, than studio rock, pop, country, etc recordings.
So, if one wants to evaluate a system for accuracy, I don’t think one can get any better than classical.
Before I got into classical, I still used it as a tool, in order to get a baseline for accuracy.