@madwolfa, yes that is a part of the puzzle for sure. I found that hi-fi pursuit aside, I was growing unable to listen to poorly recorded music, I physically was unable to tolerate it. As a result, much of my rock and pop collection is unlistenable to me. This was more of a blessing than a curse as it forced me to seek out music that I could enjoy, and that sounded good. As a result I have become a fan of new artists and even new genres that I once either didn't know about, or ignored altogether.
I think it is entirely likely the OP could find a headphone that he liked better than the HD600, it would likely not come cheap, but who knows, there are other gems out there I'm sure, it just depends on our tastes. So yes, I would say that trying new and better recorded music is while a smaller piece of the puzzle, it is still worth considering. I know it helped me rediscover what better audio can be.
Perhaps at first it was a little planned and robotic in terms of me researching and pursuing better recordings, but now these discoveries are really core parts of my collection that I enjoy completely. I find most rock and metal (I liked the progressive kind mostly) now bores me to tears. Not completely, but certainly rock and related genres just don't speak to me anywhere as much as they did. I'm sure that is not in a small way due to getting older, much of the subject matter of rock works are for younger, angrier people, or people who are constantly "Looking for A Place To Happen" (Tragically Hip reference, couldn't help myself).
Anyway, to the OP, I would suggest that to revitalize your music enjoyment, as Madwolfa suggested, might not hurt to try some new, and well recorded material.