Just a thought on an alternative: You already have 2 cards (4 mons) working. It was adding the 3rd card that seemed to give you problems. - from what I read so far. Correct me if this is incorrect. So now you are thinking of changing all cards to 3 identical cards, $79 x 3 = $240 or so. There are some USB to VGA/DVI gadgets you can use to add monitor supports. I use a couple of them made by SIIG when I couldn't get the 7th and 8th monitors to work on my new box. About $50 a piece. Normally they are not as desirable compared to a dual graphic card that sits in a PCIe or PCI bus. But they can be a solution to get around limitations. If you line the monitors horizontal in a row it is not a problem. But stacking them in a 2x3 grid may be an issue. Windows recognizes some of those USB/VGA displays (e.g. Diamond make) but not SIIG.
Yes, on the card itself... These cards have 2, Display Port, ports (DP)... so you'll need either DVI-DP video cables for your DVI monitors... or DVI-DP adapters...