The game natively supports two monitors - but - they must be connected on the same video card. You cannot, for example, use one monitor on the motherboards video, and the second on a video card. SCFA will not recognize that.
You don't need any additional software.
Some limitations. You cannot run windowed mode on either monitor - they'll both run in fullscreen. This is a problem, since if you like to alt-tab to other applications, SCFA is quite unstable when you do. Some people have little problem doing so, but many report that they become stuck on a 'grey screen'.
I've used dual screens for years, without any issue (except the above) - and frankly, I find it difficult to play without it. It's been completely stable in every way other than what I mentioned.
Now, alternatively, if both your monitors are identical, you can simply play 'windowed' mode and stretch the window across both monitors. This works (if you don't mind the bezel), but it's really still a single display. The true dual screen implementation allows completely independent views, and zooming, and tracking, on each monitor.