My ideal way of doing this would be to just stick the rio into the extra din bay and keep the old stereo/tape deck

This will only work if your existing stereo/tape deck has auxilliary inputs. If it is the deck that came with the car, this is probably not the case. If it does have auxilliary inputs, you have about a 15 minute install job. All you have to do is connect your 12V wiring (ground, memory, ignition sense, headlight sense) wires, and run a pair of regular "RCA" cables from the outputs of the empeg sled to the auxilliary inputs of your existing deck.

If your existing deck does not have auxilliary inputs, then you are faced with either replacing your existing deck with one that does, or with a pretty serious installation with external amplifier, signal switching, etc.

tanstaafl.