Have fucking have advised here. As a man, for 5 years collecting video walls and multi-monitor configuration, you comment:
-Eyefinity — will work. If you buy 4 active adapter. Along with the price card get impressive.
-Nvidia SLI — all to do with it. SLI technology increase productivity, not the number of outputs.
-Nvidia Quadro — will work, but since they have a maximum of 4 vchodove, You need two (support Nvidia I has officially confirmed that the two quadras in the same system unit earn, and the question will be whether the three said — "try it and tell us what happened, we also wonder")
-Matrox — would work well if You need to display on screens only text, static graphics or window any CAD system. If we are talking about Full-HD video or 3D games matroks not an option. Plus you can buy it in our region quite difficult.
-USB-monitors — nonsense. It is even not want to comment.
In Your case I would suggest a motherboard with 3 PCI Express and 3 mediocre video card (almost any, the main thing is to make sure they were "fine" — # 1 PCI-Ehle and had 2 digital output (DVI\\HDMI). Everything will work fine. He collected and 8-and 10-year-monitor configuration (you can give a link to the photo). Don't believe any rumors about a maximum of 8 monitors on Windows — Windows 7, this number is 64.