Its a big pinta to change anything in the logic 7 system because the amp pretty much has to go then your going to have to come up with a way to amp all your speakers . Look at the MS-8 thread it has the details.
You pretty much can only add taps of the speaker outs on the amp to add things like subs or additional amp and speakers. I guess you could do that with the ms-8 if you wanted to retain the stock head unit.
Mobridge and another(audison bit one) company were working with fiberoptic interfaces but I think its more to convert the output of the BMW Head unit to analog outputs and or process the sound.