I'm unsure why you don't see the Xfire tab to allow you to enable it. The only thing I can recommend is to attempt to uninstall the drivers and control panel and a drive sweeper, then reinstall the latest drivers at ATI website and profiles.
There are only 2 reasons for what you are experiencing that I've seen fix it. Reinstall drivers, and reseating the cards. Your cards are running at the right bus interface based what your last post, which leaves drivers or user error.