It isn't 2 separate units, it's a double-din headunit that combines 6-cd autochanger, tape and radio. I've had it apart and there are no ports on the back. I'm still not sure how it manages to hold 6 CD's in there and shuffle them about.
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Mk2a RioCar 120Gb - now sold to the owner of my old car
Rio Karma - now on ebay...