Question regarding an Aux input on my bosses car!

[jezseaton]

Guys, new here, mainly for the purpose of solving a problem my boss is having on his x5, but also becasue i was loving that thread on "cool things you didnt know about the x5"

My boss has a UK X5, with a sat nav, cd changer, tape socket behind the rotating screen, and bluetooth phone kit from nokia.
He has had a pioneer dvd installed in the rear with two screens and a wireless headphone system.
On the rear of the centre console/arm rest is a socket marked Aux In and Aux Out.
I have personally fitted alot of car audio kit (mainly in Saab's) but always remain cautious with VERY expensive cars, especially when owned by your boss
Basically he wants to feed his sony mp3 through this aux socket to his sound system.
Now having noticed the aux adaptor mentioned on the site and in the stickys I expected that this was just one mounted in the centre console.
(note opposite this button is the tv> button)
However i cannot seem to get "aux" up when pressing the mode button, have tried with no feed going into the aux in, and with a mp3 feed.
The DVD system seems very much standalone-ish, the sound from it CANNOT be fed to the main speakers.
Can anyone help me work out if this Aux input is aftermarket or stock standard (seems too well fitted to not be part of the standard system?!).
Picture enclosed.
Any help very much appreciated
Thanks,
Jez