I believe there is an API of some sort that allows 3rd party players to integrate with iTunes. The Pre didn't bother to go that route, instead choosing to emula

I believe there is an API of some sort that allows 3rd party players to integrate with iTunes. The Pre didn't bother to go that route, instead choosing to emulate an iPod. Although it's possible that the 3rd party devices are not first-class devices the way an iPod is (in fact, knowing Apple, that's almost certainly the case).