The only thing I'm seeing in the BIOS that may affect things is the "GPP slots power limit" setting. I know the PCI-E x16 specs are supposed to be for the slot to deliver 75w so you may want to try raising it up to 75. Other than that try disabling the onboard video if you haven't done that already.
In general for this problem I would think it's more Biostar's customer service you'll want to contact rather than XFX so give that a go maybe.
Have you tried using actual games to benchmark? You can use fraps or rivatuner to get an in game display of frames per second. Just disable crossfire in catalyst and check the frame rate then enable it and run the game again. The differnce should be obvious and games that don't scale in crossfire are rather rare these days so pretty much any vaguely recent game should work.
You may want to try reinstalling your drivers as well. Uninstall then boot up in safe mode and run this;http://www.guru3d.com/category/driversweeper/
Then install the latest catalyst control center from the AMD website.
Otherwise it could be something as simple as a defective crossfire link cable which would be much more convenient than a faulty card or motherboard.