Actually, You absolutely need to use 1 Display port out, one HDMI or DVI-D Out, and one DVI-A Outlet.This is due to the HDMI and DVI Sharing the same "Output connector ...???" It works the same with Crossfire on a single Card for AMD.
Beware : the 2 DVI-OUT you have are not identical, one is Digital, and one is Analogue. If you use the HDMI port, one of the 2 DVI might not work. In this case, try the other one.
SO, you may go like this.
Displayport to Displayport v1.4 Switch : output 3 Display port (tho I Couldnt find those ... -_- )
Personally at home, I got 3 ASUS VE248Q 24in 1920X1080 2ms with Displayport.
got them on special at 210$ ea. : Great Buy !!!!
This way, I use 2 DP out on my HD6950 and one DVI out. Works Flawless.
I have a GTX 680 running on 3 monitors (Connections are a DVI, DVI to HDMI and a HDMI) and It won't run at 5760x1080, as in I have no option to do so, even though my monitors normally run at 1920x1080... Why is this!? PLEASE HELP, the max res I can choose is 4523x900