Installing Aftermarket HU in '02 Z3, Need to Bypass Internal Amp

[ToplessBMW3]

I am putting my Clarion ProAudio headunit into my '02 Z3. I have the BMW wiring harness all set up from my '94 318iC, and I plugged it right into the Z3's harness. The radio works (I don't get any signal but I know I need to buy the little adapter so the antenna plug from the Z3 will fit into the HU), but when I switch to CD no sound comes out of the speakers. I'm guessing that I need to bypass the internal amplifier in the car. Does anyone know where it is and how to do this? Any help would be greatly appreciated. Thanks a lot. I can supply pics if you need them.

Sal