From what I know, you cannot use three displays with a single graphics card. The only exception would be using a Matrox Triple Head 2 Go. Unfortunately the Matrox product is expensive and does not support a digital connection. (It uses VGA instead of DVI) If you want a 3 or 4 monitor setup, you need two graphics cards, preferably identical ones. You also need a motherboard with two PCI-E x16 slots. You just use the two graphics cards at the same time, but DO NOT enable SLI. SLI only supports 2 monitors. (I think. I know it's less than 3 for sure) So you will have to run a Non-SLI, 2 graphics card setup to enable three displays.
And since you bought a computer, it is extremely unlikely that you motherboard has 2 PCI-E ports. The only options I see for you is A) The Matrox or B) A new motherboard & Graphics card.
AFAIK, a KVM switch uses the same monitor, Keyboard, Video device (monitor), and Mouse with two computers. So you can control two computers with one keyboard, monitor, and mouse. This is not what you want in this situation.