The board monitor display is pretty dumb, in that it receives commands from the buttons on the unit, acts as a display (obviously), and feed audio from the Tape, or CD player back to the Board monitor radio.

Its the boardmonitor radio thats everything connects too. The BM radio talks to the Nav computer that generates all the menus and alike back to the display. Its quite a weird system, and overly complex. This is why 3rd party developers have all sorts of funs and games trying to integrate their solutions in with the BMW one. Such as iPod integrations that can display Id3 tags on the display !!!