As of today (Wednesday) I have emailed Matrox to check if the MXO2 needs new drivers/firmware to work with Final Cut Studio 3.
Reply from Matrox “We’re happy to announce that Matrox will be supporting Apple Final Cut Studio 3. The MXO2 product line is currently in the midst of meeting quality assurance standards for compatibility with this new software release. The drivers are scheduled to ship in early September. In the meantime, you can be assured that Matrox will be providing free updated drivers supporting Apple Final Cut Studio 3.”