iXBT Labs posted a review on the ASRock A770CrossFire Motherboard

ASRock approached with maximum creativity and decided to squeeze everything possible not only from the Southbridge, but also from the Northbridge: they installed the 2nd graphics port and added nominal CrossFire support (8x + 8x), although only 790X and higher-end chipsets officially possess this feature.

ASRock A770CrossFire Motherboard Review