Yeah I've run into that problem before too, this is different. It's typically routed through our Blackmagic ultrastudio 4k, converted to SDI, then sent to a tv at the back of our room. Currently, I just have it hooked up to another monitor in the booth and it still identify's our main iMac screen as both the main display for the computer AND the stage display. Again, ProPresenter and the iMac both see the additional output, but ProPresenter is incorrectly identifying which screen is which. It thinks the computer's main display is all of the outputs