I got a DICE silverline kit which works with ipods/iphone and it has a AUX in port for my car PC project. You need to get the Ibus interface from Resler then you could control Carx with factory knobs. BUT, I think the location of that scrolling knob is not ideal for controling media when driving. I am going for the iDrive style 3D mouse that will sit nicely inside the cup holder.

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2001 4.4 Black/Tan
Sport Pkg, PDC, Cold Weather Pkg, MKIII 16:9 Navigation, Comfort Seat, Dice Silverline, OEM Running board.
Mods to come: GNET Video module, Bumblebee rear view camera, Car PC w/ Centrafuse, BU-353 GPS