I personally believe that with audio equipment, once you reach and surpass a certain price point (so that you are not listening to significantly low fidelity, distorted sound), it comes down to people own preferences of different styles of sound signatures. Sound quality is still important but IMO personal preference in sonic style trumps all that (e.g. I know plenty of people who enjoy the HD650's more laid back sound than the HD800's supposedly "superior" sound). To me being an audiophile means doing one's best to get the most enjoyment out of music (and not striving for the most accurate reproduction of recorded sound).
Even some qualities that sound relatively objective are actually quite subjective. For example, detail, most people would agree with more details = better, but often detail causes more fatigue for some people, and for these people slightly less detail is better. In addition, who's to say that the music producer intended for you to hear all that detail? I doubt music producers check their tracks on SR-009s driven by BHSE or something similar, and maybe some details you were not meant to hear, and if the original artist heard during production, they would've been removed as they were undesired. It's like using a microscope to examine a painting, sure you can see all the details but they may not be intended by the painter (e.g. blemishes and imperfections on the canvas). Now I'm not here to say high-end, detailed audio gear is bad or unnecessary, but I'm just illustrating that personal preference of sound signature is very very important.
Also keep in mind that people generally associate "more expensive" with "better" (I know I've done it). When there is a perceived difference between two different headphones/amps, people often trick themselves into thinking that the more expensive one is better, when otherwise the preference could've gone either way. I'm not saying that this happens all the time (I've been trying to stop myself from doing it), but it definitely happens (a lot).