What was needed is something like what major labels do with their "sub labels" that only release one type of music. At the same time, I didn't want to segregate each sub-genre into its own web site, which would lose much of the cross-fertilization that makes Magnatune special.
What I decided to do is add a concept of a "collection", as in "This album is part of the 'Hard Rock' collection", with "Hard Rock" linked to a page where you can listen or go to albums that are conceptually united around this concept of "Hard Rock".
Here is what the new "collection" sentence looks like on each artist page:
You can get a list of all the collections at Magnatune from: