Connector #5 in your picture may not even be enable in your 987 unit. There is some debate here whether it is a NMEA In/Out port or just used as a NMEA In port (for AIS) in some of the newer units. Either way I checked it and there is no NMEA output from this connector even with the last software update. So your choices are limited to connecting to the GPS pigtail connections for any kind of NMEA output. Just not sure how many devices you can connect to it though.