I couldn't find Windows 7 drivers at ASUS website, but try this instead:
1. - Open Device Manager in Windows 7. (Click on the Start button and choose Control Panel. Click on the System and Security link. In the System and Security window, click on the Device Manager link located under the System heading.)
2. - Once you've opened the Device Manager, browse for the hardware you want to update.
3. - After finding the audio hardware, right click on it's name and choose Properties. Once chosen, click the Driver tab.
4. - Click the "Update Driver.." button.
5. - After the window is open, choose this option: Search automatically for updated driver software.
If this doesn't work, try others' answers.