We are currently working on a project with 5 different displays connected to the same computer.
Originally we were going to use another way to make this work, untill the release of Unity 5.3 with added multi-display support.
1 display @ 3840x2160 (native)
4 displays @ 1920x1080 (native)
The thing is, that when we make a build, the 4 displays are “seen” correctly by Unity, but only display a black screen.
When we changed the resolution of the first display also to 1920x1080 it did work. So in short, when all 5 displays were using the same resolution it worked. (Also when we set the 4 displays to a forced super resolution of 3840x2160 did it work, however 1 PC with 5 ultra HD displays connected is not strong enough to run it at good enough frames.
Obviously we would prefer to set all the displays to their native resolutions, it would help a lot if anyone could help us out with why the 4 displays will not work then.