Crossfire HD 6850 and HD 6870

[Niblisa]

Hey guys, so i have AMD radeon HD 6850, motherboard is ASUS M5A78L-M LX3
and im passionate gamer that needs more horsepower. I did read that it is possible to CrossFire two cards from same series, in my case, i want 6850 and 6870. So if anyone has time, feel free to give me advice about compatibility and instalation of both cards.

Thanks in advance

 

[clutchc]

Is this your board? http://www.asus.com/Motherboards/M5A78LM_LX3/overview/
That motherboard only has one PCIex16 slot. You can only use a single card.