It can be done by having one media player encode its output for front speakers then open another media player and have it encode its output for back speakers. I spent some time searching for you but I couldn't come up with any results. I suggest instaling winamp and through winamps plug in directory online. If you can find a plug in that can direct sound for multichannel soundcard. You could then run two instances of winamp - one for front speakers and one for back speakers.
