(Part of the on-going saga of installing a MK][ in a Lexus RX300)

In my car's factory setup the CD changer in the glove box sends a differential signal to the amp for each channel, each on a pair of wires. That is to say the voltage that matters is the what appears across the two wires. The empeg's outputs as we all know are relative to ground (both the 1 and 4 volt outputs).

So how to convert the single-ended output from the empeg to the needed differential inputs? Presumable I could use some of the transformer-based signal isolators like this. But what about things like impedance and voltage levels? I can't find anything that says what the typical voltage difference is. Anyone know the specs and/or a design or source?