Dunno if this will help at all in your case but I did find a post from a while back from someone saying the only way they got some other game to work like that was to have all 3 screens on the same video card.

I know zero about multi-display setups since I use a single 29" 2560x1440 screen but maybe that can help you. Sorry I've got no other ideas.

Hope you fix it. I saw a YouTube video of the game on 3 screens and it looked pretty nice.