At last, a topic on which I have some, ahem, experience! Having been a university librarian (except we're not called librarians any more)for 30 years, I secretly regard classification of a physical collection as an imperfect compromise to try and cover as many bases as possible. After all, a book/CD may sit well in more than one genre but can only be physically shelved in one place. Who hasn't gone into a book/record shop and tried to guess which category includes what you want?

At home your filing system doesn't have to be universally accessible so put them in whatever order you can most easily live with. For me it's a single sequence in alphabetical order of artist, regardless of genre, because I can almost always remember who sang/played what I'm looking for.

I do also have mine listed in an Access database but that's only because when I was burgled the insurance company wanted a list of the CDs which were taken and I had no means of working out what had gone and what hadn't.

Incidentally, the most common unanswerable question people ask at library counters is where to find a book whose title and author they've forgotten, but they can remember it's red/blue/green.