I have a similar question. Looking at Avid’s specs for MC 6 they list the “Harpertown” Mac Pros as qualified, but only the 3.2 or 3.0 GHz versions. I have several of the “early 2008” 2.8 GHz versions. Is this just that Avid didn’t qualify my systems or is it that they flat out can’t run MC 6?
Purely speculation of course, but I suspect it will run on the earlier machines, Avid just didn’t test them. There’s already information out there that MC6 will run on 10.6.8, which also isn’t ‘supported.’