[GPSNavX]

The problem is the NASA AIS receiver filters both the Garmin proprietary data (needed to transfer waypoints, routes, tracks) and all but the $GPGLL NMEA sentence. A multiplexer (mux) will not support the Garmin proprietary data, however it will allow ALL the GPS NMEA data to be received.

I would recommend a Shipmodul Miniplex Lite mux. Run the GPS into channel 1 and the AIS into channel 3 and if you have NMEA instruments run those into channel 2 of the mux.

In order to transfer the waypoint information to the Garmin GPS, you need to directly connect the Garmin GPS to the Mac via a Keyspan USB to serial adapter. The Mux does not support the Garmin proprietary data.