VNC works ok with an empeg over a network. Why not just install a computer in the trunk next to your empeg?

http://www.linuxdevices.com/directory/Hardware/Systems/

Lots of tiny systems there. You could get some sort of a serial control pad up front in your ash tray to make the cpu switch between empeg vnc, dvd, odbII interface, whatever. Throw in an ir extender for the remote. No need for a clunky keyboard in the car. Of course, it's always a possibility for the passangers. You could kill two birds with one stone and get an ir keyboard. The extender could transmit kbd and empeg remote.

Or, if you really desire kicken visuals. Do what I mentioned above, but split the empeg output into the audio in on the pc. Then depending on the resolution you have, you could run some sort of pc visualsation program on the audio input. Either run it above/below your empeg remote, or overlay the empeg screen somehow.

Transient too! Imagine hitting a button on your empeg remote and seeing the empeg ui slide up (semi translucent!) on top of full color visuals.

This is assuming you're willing to install a computer in your trunk and can hack some software/hardware.