You should be aware that you must in effect enable it in bios first .
1. Plug the display cable into the PCIe x16 graphics card
2. In BIOS Setup, set "Surround View" to "Enabled" and set "Init Display First" to "PEG"
3. Save and exit.
If you follow the steps outlined when you re-start your PC, if you have already installed the ATI drivers, you should find that it will automatically default to Crossfire Mode. If it hasn't you should find the option under the Catalyst Control Centre.
Are you sure your card supports Hybrid crossfirex function?
Crossfire certified graphics cards:
More about crossfire function: