Sorry I dont know how to set up Nvida cards. The game does work on triples, mine works it's just the side monitor images are kind of warped and not aligned properly.
I think maybe, I saw on the Pcars forums something about setting up a profile for Pcars on the Nvida setup screen (?) Have a search for the advice over there. But it's something like setting big enough resolution to cover your three screens, for me it's like 5760x1080 or something like that.
In regards to have full support like Assetto Corsa or iRacing where you can render each screen separately and adjust side monitor angles etc etc, that support is still to come in a patch.