From another customer’s feedback. We can confirm the following connection works.
Em-trak B350 NMEA 0183 TX-(blue)
> A031 NMEA IN+
Em-trak B350 NMEA 0183 TX+(brown)
> A031 NMEA IN-
Make sure the baud rate should be set at a high speed(38k4). This is the same as Si-Tex,Watcheye, Seatracer, Comnav AIS transponders, and Standard Horizon Vhf radio.