Originally Posted by Nevcairiel
JRiver Media Center can output using WASAPI Exclusive among many other ouput modes, and directly output the right number of channels if so desired. Its not free, though.
Further, I've found iJRiver Media Center's in-built upmixer called JRSS, to be superior to Dolby PLIIx, or any format my receivers have, My stereo music and 5.1 movies are upmixed to 7.1 using JRSS and then sent as PCM to my receivers, which then apply DTS Neo:X to add height and wide channels to mix up to 11.1. The results are pretty impressive for music and video.
IIRC: Another advantage of JRSS is that if the media file is being played from within its own library, it knows whether it's a music file, a tv show/movie or a music video, and it will subtly change the upmix profile. Therefore a music video, even though it's a video file, will receive the same upmixing algorithm as a music file. Further, you can specify various DSPs and specify rules in ZoneSwitch to apply different playback rules, e.g. output channels, or ouput device based on the rules.
So, not free, but stupendously customisable.