Thanks Scott. I checked out some of the Bluetooth receivers. It's like an adapter that receives the blutooth from the phone, then converts it into analog aux output or whatever. Cool idea for us vintage types.
I still use cassette adapter in my '00 minivan.
I also learned that bluetooth is definitely a compressed data pipe, so playing uncompressed wav through bluetooth is impossible.
I also found this app, called AptX, which makes a better sounding music connection over bluetooth, if both ends are running the app. BMW system doesn't run it.
So I think the only ways to play uncompressed music are via Aux or CD.