Stereo wiring madness

I am working on fixing the stereo mess that the previos owner made.

The car has a standard svx stereo cassette and an after market alpine stereo CD. Kind of weird but it more or less works. He wired the speaker wires together so that either head unit plays throught the speakers. My problem is that I need both a CD and a cassette and I don't really want to spend alot of money. So I would like to figure out how the stock cd player turns off the stock head units sound when you insert a CD. That way I can turn off the stock unit when the alpine unit is active. Anyone know the wiring connections between the two stock units?

[Noir]

you may want to email svxdc and see if he knows the wiring between the two units. he's come up with his own wiring harness that works well. he may know the mapping between the two as well and where to get the parts to make one. you have to email him not pm because he does not frequent his pm's.