I think anything can sound "good", the difference between low price and high price is, generally speaking, better components, and more complex circuit topologies. With these two things the sound may supposedly be altered for a purpose, not necessarily "to sound better", but also things like musicality or fidelity, and I think in practice, actually a balancing act of different things by the designer. Musicality ultimately is a matter of personal preference, and insofar as you buy more expensive gear for its sound signature, you are paying extra for sound signature. But fidelity, although is most often subjectively gauged by audiophiles thus a fuzzy topic, is still a much less fuzzy yardstick for judging the "value" of expensive gear in relation to less expensive gear. That is not a comment on the degree of"fidelity" difference between cheap and expensive gear, just saying that the concept of fidelity would theoretically be a lot better measuring stick than musicality, even though fidelity is probably seldom the sole goal of an audiophile.
There may in fact be no fidelity difference between cheap and expensive gear, I do not think any scientific tests have been done to solve the matter, and it would be extremely difficult to be precise, just consider how you are to measure the degree of difference in perceived "instrument separation". So putting aside the goal of objectively knowing the value of more expensive gear, there is still the question of how much closer more expensive gear is to real life unamplified music in subjective listening, assuming all other variables including other gear, room acoustics, and recording are addressed). Obviously people who buy very expensive gear do not agree with the usual inferences drawn from RMAA measurements of audio equipment that say $50-100 gear score perfect on some things, so the gear must be critiqued subjectively, and be open to faulty perception and interpretation of sound and value. Also to judge value by "fidelity/neutrality", means you have to try to put yourself in the shoes of someone who gets expensive gear for the supposed fidelity benefits.
After my rather short experience in the hobby, if you were to ask me, What is the difference between low price gear and high price gear in terms of fidelity, I would say microdetails, subtleties, nuances. It's like paying more and more for subtler and subtler things, good for some types of audiophiles, bad for other types. I have listened to cheap low fidelity gear that was more full-bodied, dynamic and euphonic than more expensive neutral gear, but I wouldn't call the cheap gear high fidelity simply because it didn't seem to faithfully reproduce the recording, always messing with the microdetail.
