The FirePro cards can all handle 4 monitors, but it will depend on the connections in use. If you're using passive adapters, then you will only be able to get 2 (sometimes 3-4, if you're lucky, depending on the monitors in use), but it's pretty rare. For 4 monitors, you will need to make sure that you have active adapters in use for your DisplayPort connections (or using DisplayPort direct). In your situation, 3 active adapters will cover it for sure, and you can always use 4 if you wish. The card can only do a set number of passive connections at once, but 3 active adapters for your 4 monitors on your V7900 should be all that you need.
For a list of certified adapters, you can refer to www.amd.com/dongles .
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