The problem with doing an affilliate program for licensed mp3's is that after paying the artist, label and processing the margins are so slim that it's not worth the hassle unless you are doing Myspace level traffic numbers.
We are talking 10 cent or less per mp3. Ringtone programs are more worthwhile.
That's why I posted the link above for the fatmixes. It makes more sense on music/entertainment traffic than an mp3 affilliate program if you can find one. Theres only a couple out there.
https://www.burnlounge.com is one. It's licensed and fully legal.
But as I said, those margins per join are so low that you will be looking at making .1 cent per click. Not even a full 1 cent per click. You'd do better sending that traffic to Clickcash.