i have made excellent experiences with ati eyefinity graphiccards (Vram 3GB) with display port outputs and multiple matrox triplehead2go (DP Edition) attached to it, controlling up to 15 video outputs with one computer (via 5 matrox tripleheads)
sure should work. by the way, the computer running this installation https://vimeo.com/101154549 on four hd-projectors was only 800 euro including everything (ati eyefinity 6 graphicscard with 6 displayport outputs and eyefinity friendly adapters from didplayport to vga)...
INTEL I7 3770
KINGSTON 16GB DDR3 1600 8GB*2
kingston 60gb ssd
DATALAND HD7850 E6 6DP PROTS 2GB
ATX CASE NORMAL
500W ATX POWERSUPPLY
it runs absolutely stable since 4 weeks, i am sure there would be no performance problems with a six screen setup as well....
What Wetterberg said. Home-built gaming spec PC, hackintosh it if needing OSX. Big GTX card in it. I have an I7 2600k with GTX670 for this kinda stuff. I hooked up 3 tripleheads for 10 displays (3x triplehead + 1xHDMI) once for the fun of it. Maximum tripleheads I used in an actual project is 2 for 6 projectors.
As said up here, I 've had 2 and 3 tripleheads connected to a Nvidia GTX 670 for 6 or 9 projector outputs. You then still have outputs on the graphics card for a monitor display. Whether you get a decent frame rate depends on your computer hardware, the content you want to display/render and your Max patching skills...