Aye, there's the rub. None of the other products have hierarchical playlists and therefore you can't get the empeg in synch with them.

I think that could be solved by adding soup views to the empeg car player. Then for Karma -> empeg syncs, you'd have the files in soup views, and could add them to playlists later at your leisure. For empeg -> Karma syncs, you just wouldn't get your playlists transferred over, the songs could still go. There are probably technical obstacles to this, and also more conventional obstacles like the Cambridge team being very busy with real work... But I don't see why it couldn't be done.