The etr-6/10 (BBFF1) is compatible with the MFD12. If the cable went directly from the sounder to your NavNet1 than you will need a 000-144-463 "NavNet Hub Adapter Cable, 6P(M) - RJ45(M), 0.5 Meters". If the cable went between your sounder and a network switch, you should have all the connections you need.
If you have a BBWGPS (GP320B) you can reuse the antenna and connect it to Data 1 on the MFD12.
Hopefully you get all the cables that came with it. If not, you need a 000-164-608
"18P NMEA 2M CBL ASSY NN3D" to connect to and send data to the autopilot.