I have a 797Csi interlinked with a 997csi The 797 only has one card slot. networking the units only allows you to share waypoints and data from other accessories like the Weathersense. It also allows you to use one GPS puck for both units. However, the Map card data is not shared between units so you'll still have to have a map card for each or switch them between units.
I have my 797 on the bow and the 997 at the console. I have two Lakemaster MN chips and keep an MMC card in the 997 for recordings. If I see something on the 797 that I want to record, I go back and do it on the 997.
SPECIAL NOTE: Some people (me included) that have the side imaging unit on the bow with a MK 101lb max-pro trolling motor have trouble with interference from the trolling motor. I've been trying to get this fixed for over two years. It's better now but still an irritant given the money spent!