Yes, you can use any brand so long as they are the same series, i.e. both 7600gt. 2 of those gpu's will run 4 monitors so long as they are in a non-sli configuration. Another alternative would be to look at one of the 6 monitor capable gpus' from amd, something from the Radeon HD7xxx series. Although if you go this route, you will need to use active displayport adapters.