Finally did away with the motherboard manufacturers (Gigabyte) provided sound drivers (Realtek High Definition Audio) and went straight to Realtek. This is running Windows 7 64 bit.
http://www.realtek.com/downloads/downloadsView.aspx?Langid=1&PNid=24&PFid=24&Level=4&Conn=3&DownTypeID=3&GetDown=false
It's never sounded so good, and I've had to turn the master volume down ...
