I run three monitors in Windows 8.1. I do however run all the monitors in the same resolution, albeit with slightly different sized monitors. It did take me a while to get them all working together and even now I sometimes get a small glitch where all three screens go blank for the blink of an eye.
I would have thought the issue would be running a 4k display with monitors of lesser resolution? Surely a graphics card would not be able to deal with that?