Tony from what i read of your question, it seems you need a bridge script.. Even with the bridge script (which will HAVE to be manually created because i cant think of one already made for mp3) you still wont be able to do this because you will need access to the other sites database, even if its SQL, oracle whatever.. You will need access and writing the script to just take it, is illegal my friend!
But if i was you i would look into that idea about writing the bridge script because you could write something like that and then sell it on to companies such as itunes or mp3.com and they could sell the script to other webmasters for a subscription fee..
Entrepreneur and you don't even know it!