Zumo, Autocom and Factory Radio on 06 RT

I'm trying to integrate a Zumo 550, Autocom, and my factory radio all together. The only reason for wanting to use the factory radio is that it will (in theory) allow me to use the factory volume controls. I've been talking with Kieth at Tulsa Truck Center and he has been a wealth of knowledge, but I've got a few things to figure out.

On the factory radio I have AUX and INTERCOM not being used, can I input the Zumo through the radio using one of these inputs and then use the radio output with Autocom cable 1319 to run the output sound to my in-ears, allowing me to use the factory volume control? If this is possible, what is the cable that I need to run from the Zumo to the factory radio? I'm assuming it's a BMW part. The back of my radio has the standard plug for the radio controls and speaker output, plus two other 10 pin rectangular plugs that are not being used.

Thanks in advance!

Derek