For those wanting to hook-up the BMW audio system to both rider and passenger, but don’t have the BMW system 6 helmets systems.
There is a solution........get the Scala Rider G9x teamset intercom (other makes like the Sena S20 etc. might also work, but I’ve only tested the G9x)
1. Pair the main headset (rider) to the bikes Bluetooth ‘Helmet 1’ channel.
2. Pair the passenger headset to the main headset using ‘channel A’ (default).
3. Select desired audio playback on the bikes audio system, e.g. Radio, MP3 etc.
4. Now press the ‘channel B’ button on the main headset for 2 seconds.
5. Your passenger will now be connected to the bike audio, so both rider and passenger can listen to Dr. Dre pumpin some tunes......

Now lets ROCK....
(Note: The above guide is for those who haven't RTFM for the G9x)