The problem with the 2008 models is the FDIM (Front Display Interface Module) and the network that runs between that module and several other modules. It even controls the lighting of the buttons (which is why the factory audio controls don't light up at the same time as the parking/head lights).
Anyway, if you install an aftermarket HU, you'll lose the audio system info on the display panel at the top of the center console. I'm guessing that anyone with an '08 already knows that.
Someone may make a harness that provides that information to the FDIM in the near future, but, for now, only the factory HUs can send info to that display.
The connector faces and their pin/wire functions are located here.
You'll also have a grand time trying to find a 12v switched output. I did without, but at times my navi head unit will mysteriously stay on for minutes after I get out of the car and lock up. Its the RAP circuit doing its thing.
I recommend ponying up for the right harness w/ RAP circuit adapter. Cheap and easier.