very simple, your music was not encoded in surrounding sound.
to test if the sound card and the speakers working properly, you can play a dvd movie which has dolby 5.1 lable on the box. my theory is, if it works on the system testing, then it should works fine.
i am using powerdvd 4.0, but i don't know which version do you have. if you have the same version as i do, you can go to configurations by right click on the picture. then go to audio, select dolby 5.1. then you are all set to go!