I was using Nuendo 6.0.7 on 10.6.8 on a Mac Pro tower with an Blackmagic Intensity card for external video (via component cable) to a large TV, with two 30" Dell monitors, mini-DP to dual-link DVI adapters.
Just got a 12-core Mac Pro. I was going to ditch the Blackmagic card and just use the TV as a third monitor via HDMI. But, there is a bad bug in OS X 10.9.3 which prevents more than two monitors hooked up this way (see the thread:
It's not yet clear if 10.9.4 will fix this issue, so I'm thinking of getting the thunderbolt version of the Blackmagic. They make two models, the "extreme" and the "shuttle". I can't really figure out the differences, and one have any experience with these?