|Intergrated and video card can be used together but u need special combination of hardware for eg. Amd 785g and hd 4xxx.|
Another option is to install v-card with three outputs or use ATi crossfire or nVidia sli or lucid hydra.
Optiplex 780 has two outputs
The only option u have is find a v-card with three outputs, u don't need a gaming card. If u have slim version of optiplex 780 u need low profile v-card.
You know the real meaning of peace only if you have been through the war.