Video to RGB for 2003 Denali NAV

I've been lurking around GMC message boards and Video installation web sites for the past 2 years looking to get video onto the 2003 GMC Denali Factory NAV radio.  Well this weekend I finally found a site that published the exact RGBS pinouts in one of their installation manual's and a nice how to.  Within an hour of removing the radio, I had confirmed that these pins did in fact control R, G, B and Sync.  It was just a matter of time. 

I'm now wondering what mobile device I should/can use to convert my Video "composite" signal to RGB to then drive into the head unit?  I've found a unit by PAC-Audio called the VCI-GM1 which comes with a nice little ribbon cable ready to make the cut-in.  It has a "video" input (RCA) which one would think is just what I want. 

Problem:  The product (and every reference I've seen so far), markets itself as an input for a backup camera.  No place does it mention that it would be satisfactory for any type of video input.  What I would like to do is to take the Video out from my audiovox overhead unit, and bring it into my front seat NAV. 

I've e-mailed both PAC-Audio, and a guy selling on eBay, but so far no response.

Anyone have any ideas, or other alternatives?

Roveer