ALL of the 68xx cards support 6 monitors out of the box, but they need to be chained or use hubs, there are only 2 DP outputs, I believe. There aren't any special versions I know of. The AT 68xx review has a page dedicated to how they support multiple monitors and the various configs.
I assume this will be a key feature of the entire 6xxx series, but since no other 6xxx cards are released, that's only an assumption.