If your existing deck has low level outs you may connect those to the empegs aux input. There are high-to-low level converters available if it doesn't.

If your existing deck has low level inputs you can put the empegs low level outs into that. There might be an adapter that transforms your CD changer input to normal low lovel inputs.

There are RCA switches that take 2 sets of low level outs as well as the remote on wires. Output is one set of low level outs and one remote wire to control your amps. One unit is the primary - if this is on, its outputs are selected by the switch. If it is off, the other (secondary) unit is selected.

While simple Y-cables might work if you always only have on unit on, if you forget, or someone else who uses the car - you might let out expensive smoke...

Also check out the installation part of the FAQ at http://www.riocar.org

/Michael