There would be a play/stop/ff/rew on the title bar that appears when a file is linked.
You could use the same sorta code that saves annotations.
Doesn't have to "know" what song it is across all books... Just "that" sheet in that book.... And if I want, I could manually assign the single audio file to all occurrences of the sheet.
If that already exists please slap me around and link to the instructions