OK
I can't claim the credit; the solution came from Neal at Sonnet, it worked for me:
Intel machines don't use firmware on cards. That's why there is a separate Mac Pro driver. You can't update the firmware on the card because you don't need to. Even if you moved the card to a G5 or similar and updated the firmware to 2.12, the Mac Pro would still ignore said firmware.
So you have the correct version of the Mac Pro driver. 2.12 (
http://www.sonnettech.com/support/downloads/computercards.html). You might try this trick and see if it helps:
Delete and empty trash for the three (3) following files and directories:
/System/Library/Extensions.mkext (a file)
/System/Library/Caches/com.apple.kernelcaches (a directory)
/System/Library/Caches/com.apple.romextensions (a directory)
The last directory might not exist so don't worry about it if it isn't there. Restart after you do this so OS X will rebuild some of the files.
I had a weird log in screen first time round which hid my password, but got in as guest and then logged out to find that all was fine: disk utility doesn't hang and all is well