I also had your same preocupations, I contacted support almost a week ago an they gave me the following reply:
Feb 5 (6 days ago)
At this moment ASRock is waiting for Microsoft to provide certification for windows 8 drivers.
Please visit our website in the next coming weeks for updates.
ASRock America Support
Everything works except for XFAST USB and RAM. (Tried on W7 compatibility mode and didnt work either)
Feature I dont use so dont know if its working is the aux bypass and AXTU.
My specs are:
ASrock Extreme 3 Gen 3
No problems with any drivers at all. except for those mentioned above (XFAST)
Hope that helps...