So – you’re trying to dongle your way to 3 monitor goodness? Just a quick heads up – you cant have 3 HDMI based monitors connected to your fancy little trash can (Mac Pro). The systems only support 2 HDMI headers. You can have a 3rd (maybe even a 4th?) monitor connected but that have to be DVI or VGA. 2HDMI+1/2 VGA/DVI’s should work fine though.