What do you mean by "can't run them" - crashes? laggy? won't start up?

Here's my system:
i7-920 overclocked to 4GHz
12GB RAM
2GB ATI 6950
Eve on SSD
ISBoxer with the clients stacked on the left screen and a dxNothing display of 15/27/36 video feeds on the right screen

I have a 5-man team that I run with medium settings and 30/15 FPS limit - runs really well;

I have a 9-man team that I run with low settings and 30/15 FPS limit - runs well, the PC occasionally feels a little sluggish, but it's very playable;

I tried running 12 clients and although it works, the PC really has issues - after docking/undocking/gating (ie. any transition) 1+ clients will crap out, giving me a black screen on that client which needs restarting; and I've even had several occasions where some of the clients stop taking keyboard input but the mouse is fine; 12 clients really aren't playable on my PC