Here are some diagrams and pictures that might help people in their future installs.
First I took a look at the wiring harness by the amp (std. US-spec "Hi-Fi" stereo, non-L7). Wow! What a tangle.
IMG_0695.JPG
So I pried them apart to figure it out.
Wiring Harness-1 copy.jpg
Then, to avoid confusion I made this wiring diagram on the computer.
BMW Hi-Fi Wiring Diagram.jpg
Then I decided to make one to help out the Logic 7 folks.
Wiring Diagram-l L7.jpg
If I got anything wrong, please let me know and I'll revise. I was working off some forum thread info for the L-7, since I don't have such a system. Cheers and good luck.