We don't fully understand why the human brain works the way it does but that's something different from how sound works which is quite well understood. We've understood it for going on 80 years. I point at the work the many engineers at Bell Labs in the 1930s. For example, Messrs. Fletcher and Munson, famous for the Fletcher-Munson equal loudness curves. Good headphones sound good because of their work. Another example, Messrs. Nyquist and Shannon, famous for the Nyquist-Shannon sampling theorem that makes digital audio encoding and decoding possible.
I stand by my statement: audio is a well defined, well understood science.
I agree that audio is a well understood science and that our perception of sound is not well understood.
The human hearing did not develop to test out audio products, it developed to assist with the survival of the human species.
While human hearing is extremely sensitive it is subject to our psychological state.
There has been tremendous work on this by Pawel J. Jastreboff in particular when dealing with the problem of tinnitus and other medical condition. Jastreboff's work does not give detail about the relationship between psyche and audio perception but it does illustrate how massively important the psychological state is.
From Jastreboff's work we can see that humans can tune in to particular sounds, they can change the nature of sound, indeed they can do pretty much anything with sound. Very importantly, humans do this all the time and subconsciously.
The flexible nature of our sound perception probably explains many of the phenomena described by audio enthusiasts such as differences between cables and similar issues. It is probably auto-suggestion at work in most cases.
I believe that Hi Fi enthusiasts for the most part engage consumerist desires and anxieties with the business of audio perception, so that when they listen to something expensive, for example, they mobilise auto-suggestion to hear sonic improvements, when they listen to something cheap they do the reverse.
Throughout audio this problem of auto-suggestion in hearing driven by consumerist anxieties is probably causing people to spend a great deal of money and time on things that will bring no real benefits to their enjoyment of music.
In my signature I have a link to an article on auto-suggestion which expands on this subject a bit.