Many thanks to all who provided information in response to my request; it turns out to have been very helpful indeed!

My installer spoke with a technician at the Minneapolis Porsche dealership this morning, and was told that in the 2007 models, the fiber optic cable running into the back of the factory head unit is pre-wiring for the CD changer option.

My guess is that the fiber optic cable is also used to display the radio station playing on the gauge cluster, as was pointed out in one helpful reply.

In any event, it appears that this fiber optic cable does not communicate to the car and that the only consequence of disabling it is to issue an error code when the car is hooked up to diagnostic equipment, which should be easily understood as it will be obvious that the car is equipped with an aftermarket stereo.

I expect the installation to be completed tomorrow, and will report on it. Hopefully, everything will turn out just right.

Again, thanks to everyone for their help.