M’mm, this is a bit of a worry as I’m just in the process of going from FCP7 to X. In my case also on a Mac Pro and also the Blackmagic decklink Studio 2. When I installed the Decklink software I got a message telling me I needed to update the software for the card. Well the card doesn’t have software so I assume what they mean is a firmware update which I’m loath to do because I might loose functionality in FCP7 which I run on Mountain Lion from another boot disk.
If FCPX isn’t giving you the full list of output options like it does in FCP7, what if you go to the Blackmagic control panel in System preferences and check “Set default video standard as” I can’t check it myself because I removed the BM driver for the time being. Also I found that there are no bars and tone in FCPX which is a bit of a bummer.