What do you mean by 'crossfire mode'? As to the 4870X2, yes, it will work fine on your board as long as you have a big enough PSU. If you are referring to crossfiring with the onboard, only a few of the low end cards do that, and it is not really worth it in my opinion. In fact, if they let you crossfire the onboard with high end discrete, it would probably slow the system down rather than help. Sorry if that was not your question.