Bill, I have Standard Horizon GX2150, Garmin GPSMAP640 , Tacktick wind/speed/depth/temp and Raymarine SPX-5 integrated, The reason for the Seatalk-ng backbone is because the SPX-5 course computer does not supply power to the P-70 control head through the Seatalk-ng port. I first had the P-70 connected so that it got power from the Raymarine S100 remote but that didn't make sense to me because it meant the remote was directly connected to both the course SPX-5 course computer via Seatalk and the P-70 via a Seatalk/Seatalk-ng adapter cable. Raymarine Technical Support recommended the Seatalk-ng backbone.
