Team Air Cubase 5 5 2 Update
this is not an outright embargo on nvidia cards in the mac pro. nvidia does not state they are incompatible but they are not officially supported. if you know of a user of an nvidia gpu that is reliable with the mac pro, we would love to hear from you, it is helpful to us. the most common reason is the mac pro does not have an appropriate pcie slot for the gpu on all versions. nvidia's support for the mac means that to use an nvidia gpu you need to either have access to a suitable expansion card, or a mac pro with an available pcie slot and a mac compatible efi rom. we have provided a link to apple's faq on gpu lock-in if you need more information. as the nvidia video cards are older, they tend to be more reliable as the operating system is either not trying to support them as-is or don't need a video interface.
Team Air Cubase 5 5 2 Update
assuming an appropriate expansion slot is used and the mac pro has a compatible efi rom, it is possible for the machine to work just fine. however, there are some limitations with the nvidia cards being able to share space on the pcie bus. the most common issue for users is that the nvidia video cards only support 16gb of ram, which is just enough for a single user to run their application. additionally, nvidia cards are only installed in the ram slots, not the pcie slots. while we cannot be certain of why apple prohibits using multiple nvidia cards on a mac pro, the systems are free to use more than one traditional expansion card.
any users who have multiple nvidia cards and are happy with them being on the pcie buses can contact me. i can give general advise as to what the pros and cons are with such a setup for the mac pro. i have been running a mac pro with nvidia cards since the mac pro 6,1 days and have never experienced issues with more than one card. it is a possible restriction, but it is not a closed door.