Thanks for the suggestions, but unfortunately they aren't really an option for me. My current PC has two nVidia cards in it running four screens, but the whole point behind me purchasing a Haswell board was that I could get away from the buggy closed source drivers provided by nVidia and AMD. I run Linux, and on this platform Intel provide open source drivers which by many accounts are far more reliable than any other alternative, and being a programmer, it means if I encounter any problems I actually have a chance of fixing them myself without relying on the whim of some company's engineers. (I have reported a number of bugs to nVidia which took in some cases years to get fixed.)
So yes, I could stick another video card in, but since Intel don't make discrete video cards it'd be from a company with sub-par drivers so I'd be back to where I am now with less than optimal reliability.
Your suggestion of using a device which appears as one screen but splits the image across multiple monitors would actually work quite well, but unfortunately the only device I have seen that does this only supports tiny resolutions and does not support monitor rotation. Since I run a few screens in portrait mode at 1200x1920 and 1200x1600, I haven't found a device that can split one monitor signal into these resolutions - especially when the individual monitors differ in resolution.
However at least now I know there is no point in purchasing a DisplayPort MST hub, because it wouldn't allow me to connect any more monitors than the onboard connectors.
