My problem is a very strange one, I have absolutely no idea what could be wrong. So, I have a 5.1 surround system at home hooked up to my PC with Windows 7. I'm using Realtek driver, but the problem is not that. In the options panel for the driver, when I test the speakers, they all work, and make good sounds. Same happens, when I test them from Control Panel/Sounds. They work perfectly, when I play a song on Youtube. But, when I play a song from my hard drive, only the front and center speakers work. No bass sounds, and no rear speakers. I tried several players, and none of them works. I tried changing audio output, because I had several choices, like 'Default', 'Realtek Digital Output', 'Realtek High Definition Output', but no luck there. I downloaded a video in mp4 format, and there are two audio files attached, one with 2 channels, and one with 6, but there's hardly any difference, maybe the quality is a bit better on the 6-channel version. But it doesn't change the fact, that no media player on my computer can use my 5.1 sound system properly, but youtube can. What could be wrong?