Hey mate, i have done exactly this myself and the easiest way to do a single 3x3 video wall is to use 3x TH2Go units (get the DP version) BUT when displaying 1680x1050 the monitor must support 59Hz and 1920x1080 @ 50Hz so make sure the displays are compatible. Lower resolutions will display @ 60Hz. (ie: 1440x900, etc..)
Also another product to look up is Mview (They do the same products and more and at a very similar price), these guys are really helpful if you got questions. Just email them and they will get back to you (I was really impressed)
http://www.mviewtech.com/index_en.aspThese guys are even on the forums here too....
So get 3 units and setup a 1x3 eyefinity group. Everything will work great this way (Some games will detect the eyefinity group and stretch the fov vertically - I know you dont want to game..) A single 7970 will work fine if not gaming but yeah a 7990 will be much better
. But a 7970 should handle movies and youtube, etc at fullscreen.
A FREE software solution exists but currently is restricted to dx9 and d3d applications with minimal setup if you get the screens organised correctly first. Lookup SoftTH it can do cool stuff (Check out my 15 monitor setup). Once again it can only be used by certain apps, VLC works if you force d3d mode. If you are interested in this just ask...
But I think the best user friendly solution is 3xTH2G dp edition units or 3xMview units in a 1x3 eyefinity setup.
Either way you are looking around 300-350 AUD (Im Aussie...) each. This will create a single large screen and will be the most user friendly.
***IMPORTANT: A single pc can only support 2xTH2G units simultaneously so with 3 you may not have full bezel compensation (Also they must be the same model!) so I would personally recommend contacting Mview about the bezel compensation (And use eyefinity for bezel comp between the 3 3x1 display groups). I hope some of this info helps....
Oh and put up pics when your done
PS: Eyefnity is the best solution for your situation but will only support 6 max, anymore screens will need softTH and that will require some macguyvering.... Nvidia will only support 3x1 setups.
PPS: MST hubs are still in infancy and either way will only bring the total number of displays up to 6. These are needed where a single card has less than 6 outputs or if you want to eliminate tearing due to different outputs such as DVI with DP. So i would avoid these in my personal opinion.
PPPS: Xfire works fine with eyefinity (for me anyway) I had 2x7970's running a 3x3 video wall (Was using the 9 monitors in the center of my 15 setup). Farcry3 was pulling around 35-40 fps @ 3840x3072 on high settings.