This more debate over the USB / 6NR setup in this thread
http://x3.xbimmers.com/forums/showthread.php?t=521188
which is I where I read that someone claiming 6NR worked through the cable. After reading it again, I don't think it does and I assume he hadn't tested video through the USB cable.
Therefore it looks like that if you buy 6NR, BMW only wire the cradle, not the USB slot for video.
Weird as I now have the opposite in my X3 with a 6NR retrofit allowing me to use the USB cable BUT it is a Y cable with the AUX socket replaced with an AV socket to carry the video signal. I assume the reason that the Y cable is a no go in the standard 6NR setup is that you are connecting to an audio only AUX not an AV??