If you have access to Leopard install disc - I would suggest installing a fresh version of Leopard 10.5.x on a 2nd hard drive and running catalyst an older version of MAC OS than Snow Leopard.

Test the Blackmagic card on the older version of OS before performing ANY updates.

I have a 2009 MacPro running 10.5.8 (with all online updates) with Quicktime 764. - There seems to be no problems with the Intensity Pro card crashing Catalyst version m257 with that particular software setup.

Simon