Have ya tried going thru the NMEA cables,that should take care of the interface problem. I have a Raymarine gps/sounder that talks to the spare Garmin gps,Standard DSC vhfand the JRC radar thru the NMEA network of cables. The rest of the stuff talk thru the Sea-talk network off the same unit. Just a thought to maybe check further into your manual for differant hook-ups. Oh yea,check the setting on the radio to see if the coordinates are turned on.