Did you use the driver from your CD or download from GA?
I've seen where people installed both the Realtek Driver AND the Microsoft UAA Driver separately causing the same problem.
Realtek Function driver for Realtek Azalia audio chip (Including Microsoft UAA Driver in English edition)
Also, Realtek has version R2.57 listed on their site -> http://www.realtek.com.tw/downloads/
I often go the the OEM sites to get the latest drivers.