So I installed a LOC and an amp this week. I wired the stock nav deck front speaker outputs to the LOC, which then went to the amp via rca.
The amp outputs wired to the car's audio harness.

Now none of the steering audio controls work. It works fine when I put the audio harness back to stock though.

Another symptom is the speakers are really loud now even at volume level 6. I normally have it at 15.

If there is no easy fix at least for the volume, I may end up getting a new aftermarket headunit. What a waste of a decent nav unit =(

 

Looks like the 2 Scosche wire harnesses that I use don't have as many wires as the factory harness. 10 inner pins vs the stocks 14 pins. Going to try the Metra kit and see if that helps.

 

I think you need to get the steering wheel wiring option. Its sold separate from the main harness.