> Up to a point, there's an easily distinguishable sound and detail difference between cheaper and more expensive gear, given that you don't cheat (i.e. put cheaper gear in expensive enclosure), but that difference indistinguishable well before these "true audiophile" level stuff.

I don't understand how that is cheating. Isn't it a better controlled experiment if the equipment looks the same?

No, I mean "cheating at the market". Some companies sell literal snake oil for 10x the price, then they make the market unreliable for everyone, and nobody believes a company which really uses more expensive components can get better sound.

If you want a good controlled experiment, create a literal black box, without any distinguishing features, or lose the box completely and give them an output (speakers or headphones) only.

Another bad thing is, sound is so subjective and experience changes between brands a lot. For example: headphone "burn in" is considered an hallucination, it mostly is. However I have bought a set of RHA MA750i earphones which changed from "This is not what it says on the box" to "am I sure that these are the RHAs I hated" in a month, because it's sound character changed so immensely. No other headphone I had in my life did that.

So, everything is so muddy, subjective and unreproducible. When a room's organization or floor carpet density can change its frequency response, you can't control anything. Moreover, every human's ear profile is different, so you can't be sure that their ear is hearing that the same (e.g. one of my ears have a notch in its hearing curve around mid frequencies. we don't know why it happened).

If anybody wants to learn some of the tricks which can be done to get better sound, please watch Mend it Mark's video: https://www.youtube.com/watch?v=-RJbpFSFziI

While the £25.000 price tag on that preamp is literal snake-oil level and the builder has the audacity to erase the model numbers of the ICs (and OpAmps) he uses, some of the methods he uses are legit and Mark explains them exceptionally well.