I have a '94 Cadillac Deville Concours with the "Active Audio" system. It is very similiar to what you have. There are actually 3 main components to the system. The head unit, the AM/FM Reciever, and the amplifier. The head unit is of course in the dash, the reciever and the amplifier are located in the trunk. Are you simply wanting to replace the head unit in the dash and utilize the rest of the factory system or do you want to simply start from scratch?

In mine I elected to keep a factory look so I kept all the original components in place. I built a console (unlike your Eldorado mine does not come with one) and put the Empeg in it. I then put a couple of amps in the spare tire well for the sake of stealth and not wanting to cut up my car. I then wired factory reciever in as the auxiliary input to the Empeg. I disconnected the factory amplifier and ran new wires to the new speakers I added. It works great. The biggest complication was tying into the output from the factory reciever. I actually had to cut some wires in the factory harness and solder in some RCA jacks.