1) Brown is almost ALWAYS ground in our cars and certainly so in the audio system.
Power is RD/DG for battery and PK/YL/DG for switched power.
2) It has been seven years since I put my aftermarket head in, and those wires just don't look like the factory harness in my 07 SE, but again, mine is a Base model.
3) I believe the documentation in this thread is accurate:
https://www.crossfireforum.org/forum...-channels.html