So you have an FX board with an A8 processor and 6550D onboard graphics and a HD 6670 dedicated card?
If so, you cannot crossfire those two. You would need one of two things:
1. An A10 chip which is compatible with and can be crossfired with the 6670
2. A HD 6570 which is compatible with and can be crossfired with your A8 processorhttp://www.amd.com/us/products/technologies/dual-graphics/pages/dual-graphics.aspx#3