ASUS Xonar DX Prevents Sleep
When Dolby Digital Live (DDL) or DTS Interactive encoding is enabled on ASUS Xonar DX cards, you might notice that your computer no longer goes to sleep automatically after the designated inactivity timeout period. If DDL/DTS-I is disabled (giving only 2-channel PCM output over SPDIF, or when using direct analogue outputs), sleep works as expected.
On Windows Vista, Windows 7 and 8, automatic sleep will not occur when audio streams are playing, the idea being the user does not want the system to go to sleep whilst it is playing music (but otherwise idle). Most sound card drivers behave correctly and only mark themselves as playing a stream when they are actually playing a stream. This includes the Xonar DX driver when operating in its normal analogue mode (or SPDIF without encoding).
When DDL or DTS encoding is enabled, the Xonar DX driver will always be marked as in use, even when not actually playing any audio streams. The ideal solution would be for ASUS to fix their driver, but a workaround is to tell Windows to ignore the Xonar DX driver and allow sleep anyway.
Open a command console with administrative priviledges.
powercfg /requestsoverride DRIVER "ASUS Xonar DX Audio Device" SYSTEM
Verify that the Xonar DX has been added to the override list by typing:
If at any point in the future you wish to remove the override, type (without SYSTEM on the end):
powercfg /requestsoverride DRIVER "ASUS Xonar DX Audio Device"
The only downside that I am aware of from overriding the Xonar DX driver is that the system may now sleep whilst you are playing music unattended. It will NOT sleep whilst playing video files.