I think the screens you have are flickering as the TZT2BB powers up and switches resolutions to accommodate those older monitors. The TZT2BB can be fixed to a set resolution in the setup rather than leaving them to "auto". If you fix it to the correct resolution that the monitor wants, it should stop that.
If you have a TZT2BB, you can put the unit into demo mode and test if you can have the DFF3D and DFF3 on diffrent screens. I would test but my test bed is torn apart right now. I do know that because the DFF3D is a "Sonar" and the DFF3 is a "FishFinder" that you can view them both at the same time but it might only let you do it on one screen (in split screen configurations). I can't say off the top of my head if the software will let you run the DFF3D on the left and DFF3 on the right for example. Maybe someone here can tell you; or you can try it in demo mode (assuming you don't have this two units).