I just recently installed my second HD5770 card, and when I booted the computer and checked the system component list, only one card showed. However, after a couple of seconds, the screen started flickering and then the menu appeared again, now showing both cards as HD5770 and claimed them to be installed correctly.
When I started CCC though, the only place where both cards appeared were in the "Information Center" panel, under "Graphics Hardware". Everywhere else, only the card which is connected to my screen shows. I have tried unenabling CrossFireX and rebooting and then enabling and rebooting again, but it still remains the same.
I can't find out if both cards actually work together, since one of the cards only seem to appear in the hardware lists. I'd be glad for any helpful feedback.
If it added a CrossfireX to your drop down they are working. If you go into Overdrive, for example, you should now have 2 5770 cards in the drop down. You can only look at one at a time. The Crossfire option does not appear if you do not have more than one card.
Tried out 3DMark Vantage and got just above 15k on GPU-score, which is lower than I would get with 2 cards. Also, when I asked the program to check my components, only one GPU was detected and it set the "Linked Display Adapters" as false.
The first GPU test was incredibly laggy as well, white squared and lines filled the screen most of the time.