Home built Simulator

I have a 6 display out PC specifically made for gaming. Three of the monitors are used for the Cockpit panel and one to a short throw projector to project the scenery. I am able to pull out the cockpit displays out by pressing Alt and pointing the mouse on the screen i want to shift, for the added monitors. But am not able to get the scenery part for the projector. Please help.

Can you share more info on the 6 display out PC? Do you get that using 2 GPUS?