Rickie is correct.

One other issue that you may run into if you were to use one of the DI units at the console along with your 1198c Si unit: sonar interference. The DI sonar in the 788ci HD DI unit is at the same frequencies that are used for the Si sonar in the 1198c Si units. You run the real risk of sonar-to-sonar interference when running them both at the same time with their transducers on the back of the boat. I’m like Rickie and think that the 788ci HD model in the dash will work better for what you are wanting to do.

BTW: try turning on and up the Noise Filter menu setting on the units you have now. This can sometimes be used to counter the sonar interference in the 2D sonar (does not help with the Si or DI sonar).