I was just looking around for a head unit that also have steering wheel control and stumbled onto this, a DVD, GPS, Bluetooth head unit with a custom face plate for the M5.
The link to the manufacturer web page is here:
http://www.coagent.cn/view_pro.php?id=45
It sure look sweet, but it cost around $900US, a little too rich for my taste.

The link to the manufacturer web page is here:
http://www.coagent.cn/view_pro.php?id=45
It sure look sweet, but it cost around $900US, a little too rich for my taste.