The latest Nvidia GeForce drivers allow you to enable or disable HDMI Audio through the Nvidia Control Panel. You may want to use this for several reasons. First, this option will allow you to use headphones or speakers connected to either the onboard audio panel or your front panel, even though you are using the SPDIF pass-through audio connector, by simply turning the HDMI audio to disabled.
Likewise, you can switch back to the SPDIF pass-through when finished with your headphones or speakers by switching the HDMI audio to enabled. Second, this option is available for each monitor or TV you have attached, so you can enable or disable the HDMI Audio to each monitor or TV you are using. Third, this will help solve conflicts between using a onboard sound and HDMI pass-through audio. Finally, this option is located in a very convenient location to quickly change settings to suit your audio needs.
To use this option: