The key terminology to look for AMD graphics cards and more then 2-3 monitors is "eyefinity". it's mostly used to market the ability to game across 4-6 monitors, but also works for the windows desktop and applications.

Also from experience on the cards, the ones with 6 mini display port plugs tend to drive at least two screens with passive adapters out to HDMI/DVI/VGA.

Unfortunately I don't have any tips for dealing with the mess when these cards enter the marketplace via different vendors. Working in the gaming industry gave us access to the direct reference boards AMD or Nvidia creates, sometimes in a preproduction state.