Yes, but like I said: "Also, even when I switch to PCM mode and turn on Dolby Headphones, there is no audible change whatsoever. And I know what it should sound like, because I used to use analog instead of digital before I got my NFB-12.1, but DH is definitely not doing anything when I select it."
In your windows playback setting, you have Xonar S/PDIF set as default output device, so I'm assuming windows is bypassing the Xonar audio processing and send the audio straight thru the Xonar's S/PDIF output.
In playback set default to "Speakers Xonar DX Audio Device".
Windows needs to know you want the audio sent to the Xonar sound card first, then let the Xonar sound card process the audio and let the Xonar DX send the audio out thru the Xonar's S/PDIF