I have asked this and have not been able to get a straight answer. The avic 411 site hasnt produced a good answer as well. Everyone over there seems to get annoyed when you ask a question that doesnt show up in a search. I thought that was a site to provide help.
I have the D3 and the shaker 500. I want to add a sub/amp in the trunk as well. With the harness that has the RCAs, I know I have to plug those into the sub out of the D3, how do I run the second set of RCAs for the aftermarket amp? Thanks

 

The D3 has three seperate RCA outputs, for front speakers, rear speakers, and the subwoofer.

 

you can split a rca output with a Y-splitter available at any electronics store or shack hack.