First off, is Windows set(in Sound>Properties) to use HDN/Omni as its default playback device?
The vast majority of Windows systems are best off with Windows set to use the computer's on-board sound card as the default playback device. So with that in mind, could you take an optical SPDIF output from the motherboard and connect that to a matching input of the OMNI and then use the Omni's monitoring function(its SUPPOSED to allow any input to be monitored).
