I know it takes "heading" data from other compasses -- but I'm not sure if takes rate setting information that will allow it's very effcient MARPA functions to work.

I had asked, at the time I installed it, about upgrading to the B&G unit which I thought might be more "accurate" than the basic Hydra unit that I have. When I found the price of the "super" B&G unit, I decided not to pursue that. But I recall, maybe incorrectly, that the MARPA function worked best with the less expensive Furuno compass. (The installer Electronic Marine in Annapolis, who I've know for a long time, would have made more by selling me a more expensive compass. He said: "Don't do it.")

I'm not questioning the benefits of NEMA 2000. My point, Mark, is that if you cennect within a "family", e.g., Raymarine to Raymarine (current units) you'll be using their proprietary connection system. (or B&G, etc.).