So, there is an option in the network menu to select which transducer you are pulling DI from so I know you are SUPPOSED to be able to view the dedicated DI unit from the SI unit. That said, now that I'm thinking of it, I've never tried to for two reasons: 1. I don't sit at the console (SI unit) with my trolling motor in the water (I have a cable steer so I can't remote control it) and 2. When I want to see down imaging from my SI unit, I just view the down imaging the SI unit is capable of.
There may be a bug that keeps you from viewing the DI from the SI unit, but you are SUPPOSED to be able to.

