So I have a helix 9di already on the console and I am wanting to add a helix 9si. Is it ok to run two transducers off the transom? Will their be interference between units? If so, how can I install or fix settings where this will not happen?

Thanks

Why wouldn't you run the SI transducer and just network the second unit?

I don't know about the new Mega units but the Gen 1 Helix 9SI transducer doesn't have true DI just inverted Si shots.

You sure about that? Mine has down imaging and I can't find anywhere that it says it doesnt

Yep. It shows up as DI on your screen but it is really a blended view from the left and right side image views.

So if I get the 9mega I can network the transducer to work on the helix 9di? I want to run gps and down on the original and side on the new.

Correct, Humminbird has been using blended SI to create the DI view on SI units since Jan 12, 2010. Every SI unit made prior to that got a software update to add the DI view.
Only until the ONIX SI unit came out did any SI unit have dedicated Down Imaging.
Now the ONIX SI, SOLIX SI, and MEGA SI units have SI transducers with a dedicated DI crystal.

That's crazy , so let's say I get a helix 9 di model, will that have true di? And if it does will it look better than it does with my si unit?

Yes, the DI transducers have a downward oriented Imaging crystal and a 2D sonar crystal. Every Humminbird DI unit comes with the same transom DI transducer XNT 9 DI T.

Probably will. If you are using the Compact SI transducer, definitely will.

There will be a new MEGA DI unit coming out this Fall, don't know the specifics of the transducer that will be used.

Example of MEGA DI from a Helix MEGA SI unit:

BTW, Garmin's current ClearVu transducer has two slanted crystals to create what was called DownVu when they were using a single crytal.

Yes you can with a first generation Helix, but cannot view MEGA Imaging, just 455 or 800 kHz.

A G2N DI model will display MEGA DI from the MEGA SI unit.