It sounds like you're leaning towards leaving the Empeg in your car. Don't do it! NEVER leave this thing in the car! It's GOING to get stolen! Mustangs draw enough attention, then having an obviously not factory stereo just sitting there isn't going to help...
Anyway as I said, I would highly recommend against putting an Empeg in the bottom DIN. If there's any way to get the other unit to the bottom, (motorized screen or not) I'd do it. Actually, sell the damn thing and put an Empeg in there. :)
As for Ethernet in the car, see
this thread. Oh, and you might want to use the search feature on the BBS to find answers to this and a lot of other questions, it's the second place to go, the first being the FAQ section of this BBS. Basically the simple answer is that there aren't enough pins on the docking connector to allow for Ethernet in the car. A serial connection is available in the car, though. My installer fed the serial connector down so it's easily available. So syncs done from a laptop in your car would have to go over serial, which is a little slow.
But that shouldn't matter because you shouldn't be syncing in the car. Bring the Empeg to your PC and sync USB or Ethernet. Done deal.
Hope all that helps.
-Tony
MkII #554