So did a little more investigation on this. I ejected the harness from my Alpine amp. Oddly enough it is a 36 pin harness that was supposedly used with the Harmon/Kardon equipped X5's according to
this writeup.
Another strange thing I noticed is that my harness is one piece, not two.
I have read that some of the amps BMW have used turn on when it senses line level input, or they are always on w/ACC, or it is turned on by the radio control unit. I haven't been able to find a full pinout description for these plugs. I previously tapped the subwoofer outputs and ran a remote wire (from the white wire) to my MTX amp that powers my sub.
Regardless I need the RCU to power on with my Eonon head unit. I think
this writeup re-affirms the fact that I need to connect pin 5 (violet w/white stripe) on my old styl 17 pin harness to my HU remote wire...
For a quick test before running the long remote wire I can try connecting this pin directly to a 12V source (such as the battery that is right there) and see if it then stays on without the boardmonitor plugged in.