You need codes. Best thing is to get rid off all codecs that you have installed. Than download and istall this:
http://www.bestdownload.com/view.php?detail=750
This is the Gordian Knot codec pack. Features all the codes you want to use.
If you don't know what a codec is, don't worry just install the pack and be happy.
If you want to have sourround sound from stereo sources you should loook out for the Matrix Mixer. Great Program.