In 'theory' - so long as you have the mac drivers (if any) you should be able to capture video via firewire, in the same way you might connect a firewire video camera...

HOWEVER, it depends upon the resolutions supported by the canopus box as to how successful you might be. Try 720p (I doubt you will get 1080p) and set the computer connected to the HDMI in to the same. You should be able to select the input in catalyst once connected

Im looking at the same scenario, but using a Decklink intensity PRO card - haven't had a chance to test it yet...