You've just discovered a few VERY cool CD's that you'd like to listen to while on the road. You've an Empeg in your car.....

That's what the Aux-in is for. Hook up any CD player to the Aux-in.

I just recently ran the aux-ins through a hole in the back of my dash storage pocket under my player. I can now hook up a portable CD player whenever I want. Works great.

I'd like an interface to directly control a bmw 6 disk changer. I'm a programmer,

It will take more than programming, it would take a hardware circuit interface as well. Please see this FAQ entry.