Hello Lapworth,
Well, first off I would buy an Ethernet DI Si unit compatible to your 1198. Something 898 series or above. This is just a matter of size and how much you want to spend. A lot of options and good prices out there right now to choose from... Second, your going to need a 5 port Ethernet switch if you want to run your Ipilot Link and share info between the 2 units. Third, you will need Ethernet cables that will run from your mounted E-switch to your units. Many lengths available. Also with the E-switch you will be able to eliminate your 1/2 switch as you will be able to select these transducers to either Ethernet unit. Keep in mind that software has a lot to do with your units working together with Ipilot Link. I hope this helps, Greg would know more specifics than I do without having to look it all up.