the proprietary interface he was referring to is on the Ipod. He means the part you connect to your computer with on the Ipod.
This cable will work if you just want sound (you can get the same type thing at walmart for $5):
http://store.apple.com/us/prod...cxNzI
Something like this if you want video (I don't think you need the USB part of this, but you get the idea):
http://store.apple.com/us/prod...M1MTU
Plug either of these into the AUX jacks in the back of the center console (in the back seat). Once you plug in use the source button on the steering wheel to select AUX source. Enjoy your music.
Hope this clarifies.