Ways of getting more then 2 monitors are
2 graphics cards
specialty items form matrox
or ATI's cards with a display port as display port has it's own controller and thus is not limited to the graphics card's 2 displays via DVI,VGA and HDMI
As far as the 57xx series doing it as long as they have a display port they can do it.
But note if your monitor does not have a display port you'll have to buy an active converter which will cost around 100 dollars US.