sirius
Save yourself some money  - get an adapter from either blitzsafe or soundgate ( any good car stereo store has these, or off the internet) and buy a sat tuner plus antenna.  Right now you can get a Kenwood sirius tuner for free - promo - is you start service within 30 days
Adapter goes into BMW wiring in trunk, my local car stereo shop said the adapter is about $100, you can get off internet for $75.