My experience is that the A/V receiver is best set to digital surround or its equivalent and all special effects turned off. Different audio modes such as stereo can be selected later, if required by a specific source, but full surround (5.1, 7.1) is the best default. The A/V receiver DAC should be able to detect the type of digital audio input and adjust its mode as necessary. That goes for everything including PCM, various DD and DTS modes, DD+ and uncompressed audio. If the receiver cannot handle certain digital audio protocols they need to be deselcted in the playback software.The correct digital audio assignments need to be made in the A/V receiver setup though the default may be correct for HDMI. (That could be an issue it it was changed or ARC is being used.) Once done, if DD is not present it will be a HTPC misconfiguration. As I said before, audio passthrough needs to be set in several places, the correct audio drivers need to be installed and the correct windows and playback software audio output device needs to be selected.