Just heard back from him. For anyone else with this question, the answer is to use his 16-pin adapter, which plugs into factory on one side and has RCA jacks on the other for plugging into the HU RCA jacks. He can also add wires in that adapter for the parking brake and reverse signals, so it makes it very easy to hook up to your new HU.
That adapter along with the 20-pin adapter make it an easy hookup. Of course you'll have to follow the directions, but it is not too difficult.
I bought all the cables I needed from him and I highly recommend him to anyone else taking this on. He's been extremely helpful all along the way.