I believe the nmea allows sharing of sonar imagery, but with gen2 and carbon, you may only be able to see the 2d and not all the other screens. I hook both networks on my gen3, which is dumb. They should have one network to do it all.
Transducer/sonar sharing is done through the Ethernet cable, NMEA will not allow this. Sharing map cards, 2D sonar and StructureScan as well as full waypoint syncing are all done through the Ethernet network.