Who said it could not be done with an nVidia GTX card? Here is a card that I just found that has a single nVidia GPU but can support five displays at the same time. It is an GTX 560 Ti 384 core unit with some additional circuitry. It is a Galaxy 56NGH6DM3TTX MDT X5 GTX 560 Ti (Fermi) Multi Display 1GB 256-bit GDDR5 PCI Express 2.0 x16 HDCP Ready Video Card I do not personally know the Galaxy line so their quality and the required additional software are gray areas. If anyone gets this unit I would definitely very carefully unpack it and store all the packaging and accessories in case there is any Premiere compatibility problems for a potential return.. If you do buy this unit you might let the forum know how it works for you. It is reasonably priced at $313.
I found the card you were looking at, and see it has 4 HDMI out, and one DVI.
Impressive. I wonder if it would work. I'd love 1 card with 3 heads.