5.1 System, Everythings works, exept music

Iv bought a Logitech X-530 5.1 Sound System a month ago and used a 5.1 C-Media Sound Card witch is very old, 2002 or something. Everything worked but the sound card was way to old and i cold hear weird noises come from my speakers so i decided to remove it since my motherboard advertises that it has 8-Channel (7.1) HD Audio Subsystem. (it has only 3 audio outputs).
Plugged all the cables in, inserted my Star Wars DVD... everything works perfect. Then, i went on youtube and tried to listen to some music and i noticed it only works in stereo. I know Flash can't handle 5.1 but whit the old soundcard all the speakers were working, now only the left and right speaker work.

I also messed whit the driver and the 5.1 works flawlessly, If i press the Left Speaker, the left speaker works, if i press the right rear speaker, the right rear speaker works, if i press the subwoofer, the subwoofer works etc...
But on youtube, or other mp3 files, it only works in stereo. how can i fix this? (Also tried the speaker fill... it just sounds weird.

Motherboard: MSI G31TM-P21
Sound Driver: Realtek HD Audio Manager




Sorry if i did not post in the right section.