Bluetooth audio quality is a bit poor compared to an AUX or USB input, anyway. I have iDrive but I keep all my mobile music on a USB stick. Not a great option if you want to play streaming stuff like Pandora, of course.
There are some aftermarket NAV units out there, though, that could possibly suit your needs. But what little I've read about the audio quality is not promising:
http://e84.xbimmers.com/forums/showthread.php?t=757576