Getting depth info on my Garmin GPS

I have a Cobalt R7 bowrider, with Medallion gauges and a Garmin 741xs. I recently installed the Garmin and got that connected in to the NMEA2000 network and can now see some of the engine info on the Garmin gauge display. What I really want to do is to be able to get the depth sounder information on to the Garmin.

The Medallion gauges are combined analog and digital. One is an analog speedometer, the other an analog tachometer. The Cobalt manual tells me "the gauge system consists of a single Data Interface Gauge (DIG) and several auxiliary gauges. The Data
Interface Gauge collects information from the CAN bus and analog inputs and drives the auxiliary gauges via a low-speed data bus. The auxiliary gauges receive power from the Data Interface Gauge."

One Medallion gauge can display the depth information, along with water temperature, oil pressure, rudder angle and a host of other information.

I am trying to figure out how I might tap into the bus to get the information to the Garmin, via N2K or 0183. Has anyone done something similar? I have an Arduino / CAN bus rig setup which I can use for probing around - what format might I expect to see on the bus going to the gauges?

Any help / ideas appreciated

Thanks

Anthony