Actually the MFD2 only has one Aux input. The only other being the CD changer.
What you are seeing on the MFD2 screen is the option to have the AUX input transmit only sound or sound and Video (AV). It's still only 1 socket on the back but it can be configured in 2 ways.
If like I did, you have a video in motion adaptor fitted, then you can connect just about any audio or video item that has Phono inouts (red and white for audio and yellow for video).
As Camel rightly said, there is no control from the headunit over what ever is connected to the AUX socket and it doesn't give out power to change anything. It worked really well for me as I had a 120GB mobile mutimedia player connected (A Dvico unit) that I rigged up a switched 12V charging circuit via a modified Dvico cigarette charger so that I aways had power to the unit (the Dvico has no internal battery so must be powered at all times). I also rigged up a small IR magic eye so that using the Dvico's remote control I coul djust point it in the general direction of the headunit and it would control the dvivco. I've attached some photos below of the unit working. In this instance you would obviously set the AUX menu to A/V (Audio and Video). If you were just connecting an MP3 player (no video) then just select the Audio settig in the AUX menu and it then won't change screens.
The CD changer can be swapped for the VW Ipod dock (which fits in the same hole) and uses the CD Changer socket at the back of the MFD2. It's OK ish. It does fully charge the Ipod and switches it on and off as required. You only have access from the headunit to the first 5 playlists on the Ipod, as it emulates a CD changer. unlike a CD changer however, you can make the playlists as large as you want with whatever tracks you want. The MFD2 will just show Disc 2 (for instance) and Track 10. It does not show track names. It's a fairly decent halfway house between the CD changer and the MDI implimentation of the RNS-510.
I've now swapped all my MFD2 equipment for an RNS, and it's briliant, but I do sometimes miss the convenience of the Dvico unit though.
Hope this helps.