WASAPI

WASAPI is Microsoft's method for delivering an unmodified bitstream to a sound device. It was first available in Vista. MC13 added support for WASAPI at about build 100.

For XP, ASIO is similar.

An Interact thread on WASAPI can be found here: http://yabb.jriver.com/interact/index.php?topic=48478.0

And here's a personal story from a user, jmone:

"My HTPC is connected to my Receiver using HDMI for both Audio and Video. I have configured Vista Audio Mixer for 5.1 (as the default) and have all my software apps decoding and outputing LPCM using WASAPI Exclusive as the audio renderer (JR WASAPI for Audio Files and Reclock for DirectShow playback). I use my HTPC for playback of all media types including Audio (CD, CD Rips, mostly in 2CH), DTV (can be in 2ch or 5.1), DVD / BluRay / Movie files (can be in 2ch or 5.1) and this is where WASAPI Exclusive is terrific as it will configure the output to the correct number of channels. The real problems it has solved for me is 2ch TV and Movie playback where the "blank" 3.1 channels stoped the Receiver using the Subwoofer for base mgt and the Center Channel for dialogue. At my age I certainly will not claim "goldern ears" and can not say that the quality between the available renderers is apparant to me. I do however easly notice the incorrect handling of 2CH material broadcast over a 5.1 configuration. Even 2ch audio sounds "better" to me when the Receiver is just getting 2ch input not 5.1 from MC." (from this thread )