NV can only run 3 screens with more than 1 gpu. With ati it's possible to run 3 off 1 gpu.
However, both ati/nv gpu's only have support for 2 native screens so any more must use displayport.(and an active display chip should you wish to convert from dp to dvi)
Thus, nvsurround/3+ needs 2 gpu's and uses the dvi port on the 2nd gpu and with ati you can get away with eyefinity on a single card but you have to use the display port.
1 of the dvi ports of the 590 will be connected to the 2nd gpu for nvsurround on a single card.
