Mixe, welcome to the forums.
No promises but give the Via driver from this board (M4A78 Pro) a try,
ASUSTeK Computer Inc.-Support-
The only difference I can see between the one on that board and yours is your is the VT1708B, and the other is the VT1708S. If you get the reference driver from Via it is for both solutions, so there is a very good possibility that the driver from the link above will work with yours.
P.S. That is also the board that I have, and as for how well the Via sound works I couldn't tell you as I never read much of anything that had anything good to say about it (think along the lines of how bad Realtek was a couple of years ago) and have never even enabled to to test it.