Hello, I have exactly the same Problem
I have an ASUS P7KC motherboard with a realtek HD audio chipset. When using windows 8 and windows 8.1 everything was fine with the default windows whql driver. After the 8.1 update 1, the sound quality was really poor, almost like a radio/one channel output. I uninstalled the driver, rebooted the computer, windows re-installed the same driver and the sound was the same. So I went to the realtek download page to find the driver for the audio chipset : Realtek
They say it is windows 8.1 compatible, but not windows 8.1 update 1, but I tried though. It installed smoothly, no errors during the installation. But after a reboot, the sound quality remained unchanged. So I installed the same driver in compatibility mode for Win 7, and after doing that, I had the realtek icon in the bottom right of the screen that appeared. Thanks to that icon, I have access to the equalizer for setting up the outpout audio quality, now I have "almost" the same sound quality than before installing the update, but I've never had to configure that to have a normal audio on my comp.
I believe the problem we have is specific to the audio chipset used.
Laurent
