Crossfire is a bit iffy from what I've read in the past when you try to do different cards together. I would have assumed the latest drivers would do the job fine.
Have you verified the card is working when it's the only card in the system? It is possible in the first board that the 2nd PCIe slot wasn't providing enough power (even with the external power plugged in).
This is hybrid crossfire - The A10-5800k's 7660D GPU crossfired with the 6670.
I did try the 6670 on its own with the MSI board and it froze up whenever you got about 10 seconds into any game on steam.
The MSI board only has one PCIe slot - In order to enable Crossfire with the iGPU you have to enable a feature in the Bios, which I did. I then disabled it and tried the 6670 on its own and still froze when gaming. It did not freeze while using the PC and on Youtube odly enough.
Like I said in my other thread, this is more just something to do and test around with, but still, It looks like I bought a 6670 from a unresponsive ebay seller.
I'm switching later tonight to the ASRock board, and was going to do so anyways. Hopefully it solves the issues. IF not paypal is going to get involved if I don't hear back. (It's already been 48 hours since I emailed the seller - no reply)
EDIT : THis is the card -
http://www.newegg.ca/Product/Product.aspx?Item=N82E16814103198