Actually Ofer and Alex are still working on it. I'd been regularly following it on c5. It boiled down to this.
GM changed the wiring so much that the tech manuals no longer work, and you can no longer plug in the 4 pack gauges in the center. It took him a few months, but the data cable to plug in the 4 pack gauges is now under the passenger side kick panel.
Alex and Ofer purchased the main wiring harness and started tracking down all the wires.
Ofer found who made the connector so he was still working on it in order to make a harness.
It was unknown at this time if you need the dealer involved to program anything on the unit, or if the unit directions display on the HUD. I suspect you will need them to program the onstar to the radio, as I had the dealer replace my onstar under warranty and they had do that for me.
Does that help?
Ofer is 2ssrs and runs gen5diy.com