See also:

Priority options
The driver has priority The source selected via iDrive in the front is output on the vehicle loudspeakers and can be selected but not operated from the rear. Other audio or video sources ...

CD/Multimedia
CD/DVD drive Music collection External devices Tone control ...

Enabling operation in the rear
Only possible via the iDrive in the front. 1. "Settings" 2. "Allow rear control" 3. Select the desired priority. ...