I recently found a fairly big breakthru on this info. The harness that has 3 rows of pins handles all the communication of the factory USB, AUX, Steering Wheel Controls, Handsfree Mic, and possibly CANBUS info.I did the maestro idatalink MMR module myself. I only get a few on screen accessible choices. I can't access the rest of the gauges cause I don't have the 100% info/wire hook ups/schematics or can't get it from online searches. Hence why a professional will be required for full 100% use of available gauges.
For a long time I was unable to find the male side of this harness so that I could connect to all those functions with my Pioneer AVH-x7800BT. Then thanks to RichardNixon I was able to find this adapter. I'm going to be wiring up everything is weekend with a beauty harness. I'm going to take pics and make it's own post as well.
AUDI 20 pin harness