I guess I missed this. I played the Steam version yesterday and discovered that the version on there seems to be more advanced than anything that had been released here. There is full cabinet support with 3 monitors. I am able to use the buttons on my cabinet because they are mapped to keystrokes and even nudging. I am not sure how long it has been there but I have not seen any mention of it here. There is even some help going on at the Steam forum. I am not sure if it is the developers or just helpful users.
Apparently I missed the announcement that the game release and support is moving to Steam instead of this dedicated forum site. Did anyone else see it? Would have saved me a whole lot of headaches and concern.
If anyone is interested, you can get 3 monitor support by right clicking on Pro Pinball Ultra in your library > Properties > Set Launch Options > M3
I would guess you can do the same for 2 monitors with M2
Sorry if this is old news but I was totally unaware.