How to Enable Realtek Digital Outputby Todd Bowerman
If your motherboard uses a Realtek sound card and supports digital output via optical or HDMI connections, you have the option of using that digital output as the primary source of playback from your PC. Digital output is enabled by default, but driver downloads and other system changes may accidentally disable it without your knowing. You can re-enable Realtek digital output from the Windows 8 playback menu.
Go to your Windows 8 desktop by clicking “Desktop” on the Start screen.
Right-click the “Speakers” icon and select “Playback Devices.”
Right-click the Realtek digital output device and select “Enable.”
Click the “Set Default” button to make Realtek digital output your default playback device.
Click “OK” to save.