I have a Garmin GPSMap 4208. The manual gives the impression that it can only link with Garmin autopilots. This is not so.
My autopilot is a 5yr old Raymarine P70/ST400, and it can take a heading from the 4208.
Also, the 4208takes inputs from my 10 yr old speed, depth
& wind sailing instruments - all ST60 - and displays them
Just one thing: Raymarine uses proprietary, different configured NMEA200 plugs/connections - even between different generations of Raymarine kit.
AFAIK, Raymarine has a history
of 3 versions of NMEA2000 connectors
To get Raymarine to "talk" to other brands or generations will require converter connectors. For example, the ST60 instruments need a converter to talk to the P70
BUT, once you have the right connectors, they communicate seamlessly.