Multiple capture cards

Hi,

Does anyone know of a way of capturing from multiple graphics cards into a quartz compositions?

I would ideally like to capture from five black magic intensity cards at once into quartz. Hardware wise I was thinking of a mac with a thunderbolt slot and using a couple of these http://www.magma.com/thunderbolt.asp external PCI express boxes daisy chained together to give the necessary PCI express slots.

If enough PCI slots could be made available would it possible to individually address the capture cards to select them as individual inputs?

Cheers,

Colin