This thread on page three might be of help.

Using a non-Starfire reciever on a Greenstar console

There is additional information in the posts below it.

Outback sells the cable you need to go to the Greenstar. You can order it off their web site or from your outback OGC.

Outback greenstar cables

We just finish hooking up our Outback to the Greenstar I today and Darrin took it outside and we had gps signal to the greenstar. We used the Outback harness. Ours used the one that had the DB9 on the Outback end and two pins that go into the Greenstar harness on the other end. I see they offer another cable on the Outback site for another model of Greenstar and I have no experience with it. 

John