I think the satellite prep provides an additional input option that could be Sirius, XM, iPod or whatever. There are adapters made by folks like Blitzsafe specifically for BMW that integrate XM and other devices directly into the car audio system controls to include the steering wheel controls. With the satellite prep I am hoping to take advantage of this option for XM and bury an XMDirect receiver in a remote location.
http://www.blitzsafe.com/blitz_catal...z_catalog.html