There are some Garmin product that will interface directly through your Garmin network, just plug them in and they are plug and play. But some are not directly compatible and have to, kind of link, using a NMEA 0183 connection.
If you go to the Garmin home site, click below and choose the "support" tab, you can download all the manuals and ask questions directly to a Garmin tech.
They can help you identify a network compatible Garmin upper station unit. It does look like the Garmin 740S supports NMEA 2000 networking, but I would confirm that with Garmin before buying one.
Product Support Page