Route Windows 8 sound to DLNA device
I just tried Stream What You Hear with OpenELEC as the audio target and it worked out-of-the-box. AFAICS it's not implemented as a sound card device, but it seems to do the trick:
Stream What You Hear (SWYH) is a Windows application to broadcast the sound of your computer (ie: “what you hear”) on an UPnP/DLNA device such as TVs, amps, network receivers, game consoles, etc…
(from the About page)
And it's free :-)
Jamcast does PC desktop audio to DLNA devices and has a free version with 30 minute time limit so you can try before you buy.
http://getjamcast.com
I use this to play Spotify to my Samsung HDTV and now also my Xbox One.