Hello,
Chewy you are correct, thanks for the correction. 1,1 and 2,1 are 32 bit only.
So if those 3,1 models can run 64 bit then you must have a mitigating factor why you say you can’t upgrade past os10.5.x. That OS is too old for us so I’m afraid I can’t help any further. OS10.8.5 with nuendo 5.5.x has been very solid for us.
Hugh