Well I am one very happy camper! I finally had my Empeg installed and I have to say that this might just be the best $300 investment I ever have or ever will make.
Ostensibly, I thought that installing the Empeg into the factory harmann/kardon system would be next to impossible, but it turned out to be little more than finding a very knowledgable installer and a few important components.
Since I searched around quite a bit without finding anything on installing a new head unit into the factory system, I'll try to give a quick write up for future reference.

The components required are
a BMW wiring harness (p/n# PC-2-05-4) that's an ISO to ISO for an ultra clean install
a Line Driver for the factory amp (I know the empeg is 4V out, but BMW uses a high powered factory head unit, running like 8V so you have to give the factory an the extra juice.)
An SWI-X steering wheel IR module (this is a must, and the steering wheel controls can be used for volume, track back forward, pause, and enter. It's Swweeet!.)
Other than that, everything is strait forward, no need to rewire the system, or mess with anything that you don't want to mess with. Attached are a few pics of the Empeg in the Bimmer. Enjoy.

Collin

(I'd just like to talk this opportunity to thank you Tony for all the work you've put into the veritable cornucopia of an FAQ. Keep up the good work!!)