I bought a DN2820FYKH (baytrail celeron) and hooked it up to my Dell 2408WFP with sound bar and installed windows 8.1 PRO on it. I installed the latest bios and drivers from the intel website and have all windows patches installed. In the NUC the HDMI audio device is not showing up in my audio playback devices (neither is my monitor). I followed the FAQ instructions and removed and reinstalled the intel graphics drivers, no difference.
The sound bar worked fine when connected to our old toshiba laptop on windows 7 via HDMI and both its ATI card and the monitor would show up in audio playback devices in windows 7. I.e. the problem is either with windows 8.1 or the NUC.