Hi, After viewing some of the high definition wmv files from microsoft, I noticed that wmv-hd doesn't use dolby digital (AC3) as the audio format, instead it uses WMA Professional 5.1 channel audio. Which meant I wasn't getting multi-channel audio sent to my amplifier via the S/PDIF cable - I was getting stereo. Damn! A quick use of google and along came ac3filter to my rescue - it converts the WMA 5.1 audio to dolby digital on the fly (much like the newest nForce montherboard sound chips). This is how I did it: From http://www.avsforum.com/avs-vb/archive/index.php/t-403818.html Install the latest version of ac3filter from here: http://ac3filter.sourceforge.net/download/ - I'm using ac3filter_1_01a_rc5.exe Then in the configuration options: Main tab: 3/2+SW 5.1 channel PCM 32bit SPDIF disabled box checked System Tab: Use AC3 filter all boxes checked prefer AC3 encoder & and use dircetsound enabled Then change speaker setting in the windows control panel (sounds and audio devices->speaker settings->advanced) to say you have 5.1 speakers. Works like a charm and saves me the hassle of extra cables.