Hmmmmm........You know what??? I thought you wanted to run the game on one monitor and have some other software showing on the other. But, it looks like you want the game spread out across both monitors. Is this correct?? I really don't know what SoftTh is. Now all I can do is offer a few suggestions that may help. I've been using dual monitors on and off here but not like you want. Maybe try uninstalling that SoftTh. You might have to go into Nvidia control panel and set the resolution to equal the size of both monitors put together and make sure the game is set the same. You can make custom resolutions in the control panel but I'm not sure how that works for the game. This is just a guess
I have never tried what I just explained for you to do. Good luck!! P.S. Sorry if I got your hopes up.