1) do you need to tell the HU anything special when you use this adapter? When I select CDC i get a message of no CDC on the head unit. I was actually thinking of running my cellphone to the radio this way. I am currently using the standard connectionand find the sound volume too low.

2) The shielded mike cable goes from the mike to the db25 in the rear. The mike is either in the A pillar or in the center head console in later MY's.

But there are 4 pair connections from the DB 25 in the trunk to the RJ45 connector in the arm rest which could be used to route audio from armrest to trunk. Likely not shielded though.

Barry in Toronto 2001.5 A4 1.8TQ tip
Segrams Crown Royal Ashtray mod.
Integrated Sanyo 4000 CellPhone mod.
GPS Cup Holder mod.
Remote windows mod.
One touch unlock mod.