I have this cable:
http://cgi.ebay.com/ebaymotors/AUDI-...fAudioQ5fVideo
Which runs from the box to the CD changer round DIN plug.
Cheers,
Richard.
EDIT: Just looked at some other cables on there.. There's two types.. one square, one round. I assume yours came from a VW setup or maybe a more modern Audi.