Did you consolidate your itunes before backing up?
This puts all your media that is in iTunes into your media folder in MyMusic.
It leaves the originals in their place too.
Then export the library.
This gives you a file that keeps you artwork, playlists etc. etc.
Then when you back up you replace all the files, in other words replace your empty MyMusic folder with your back up and import the library again from your backed up file.