First off you need to make sure they have crossfire capability and have the crossfire bridge. If your cards are crossfire capable and you have enough power to run them then yes you can. However when crossfiring it is recommended that the cards run at the same memory and core clock speeds because if they do not they will always run at the lower speeds of the two.
I'm new to this crossfire thing
Yes both have the crossfire capability
Should I download both drivers or only one of them?
Thx I will ^^