[psygnosis]

I think some of the E60 cars that were produced around the time the Z4 was winding down had that as an option for iDrive. It looks like only number 2 in the picture is relevant to the Z4. The radio in the Z4, nav or not, wont make use of anything over USB.

The aux socket looks like a nice option for those that don't have an 07/08 to add a more OEM look. I tried to find it when I was adding aux to mine, looks much nicer then replacing the ash/coin tray. Just need the panel under the A/C controls and the cable to go along with it.

edit: just to note, I have had no issues with the AUX jack I installed in my car. With an line out dock adapter for my iPod touch it sounds great!