I can't help immediately with your digital output requirement, but I will be very interested in this. I have just bought an E36 M3 which as I understand it has an Ibus CD changer. If I could control the empeg with the standard radio that would be cool since I'm loathe to start hacking away at the dash of my $50k car.

I assume you have an E46 (3 series) or E39/34 (5 series)? Are you getting track titles etc on the head unit/on board computer? I don't think this will be possible with my E36 but I will be investigating.

What do you actually need the digital output for? As I understand it Ibus is merely 9600 baud async serial.
Edit: I see why now. I wasn't aware of this requirement in Ibus.