I'm on the path of doing the same thing here. I've got quite a way on my project.
So I've set up the audio files as Product, Albums as Product Kit. I've added a computed field to the Product Kit that displays a view of Products referencing to the kit, using nodereference. This gives me a nice display of all the individual audio files belonging to an album, with the 1pixelout player for the 30-second samples I've added and a direct button for "add to cart" for the individual tracks.
I've also created a genre view using views bonus pack Grid view. This displays up to 16 albums in a grid, showing their covers in an ImageCached fashion, sorted by publishing year. Very nice overview.

I've also added a content type Band, with each product kit referencing to an artist. Using the same method for showing audio tracks for albums, I can display a list of albums this artist has produced. Views+nodereference+cck is extremely powerful.

Instead of using taxonomy for labels, I've made a content type for them. This allows me to display all the albums that have referenced to a specific label, inside the label's node.

One feature I still want to enable is to create a playlist of all the mp3-files purchased, and send this playlist to a flash-player, preferably in a popup screen, to have a playlist of all purchased media and play it while surfing the site (or any other site..).