I have like 9 year old Radeon card which have outputs for basically everything here like 4 display ports as well as some other things like DUAL DVI ports so total 6 monitors, but I never ever used them, I do recommend not more than 2 monitor per card.
That is the same analogy as saying your car is old and it came with 4 wheels but i only drive on 2 wheels. lol ...
continue .... more monitors ---> more profits. If you want to have 2 graphic cards in a comuter, it must be SLI/Crossfire capable. SLI is NVIDIA's multi-GPU solution whereas CrossFire is AMD's multi-GPU solution