Tim,
My 2 (right and left) SI units are hooked up together with a Y cable. So I have one SI cable and 1 high speed ducer that runs to the back of my Helix 12 Mega SI G3 unit.
I have not been on the water yet to see how it works yet.
I just got off the phone with Humminbird Tech Support and they told me there is no way to run three transducers to one head unit. Just to be clear, I am trying to run a L and R SI transducer and a highspeed transducer.
I am running the Helix 12 SI G4 at the console. I am not very technical so if anyone could provide photos of their setup that would help me a lot.