I just formatted the system and reinstalled everything but the audio output is not functioning as it should do. This is the system I use:
- Abit motherboard with High Definition Audio on-board
- S/PDIF interface which is connected to my receiver/amplifier which in turn is connected to my 5.1 speakers.

Software:
- Windows XP with SP2
- Latest Realtek HD Audio drivers & codecs installed.
- Playback via Winamp 5.12 (Lite) and iTunes 6.0
- AC3Filter and WinampAC3 playback plugin installed - these haven't really caused any noticeable change.

Now the problem is that when I play back mp3's they either only come through my L+R speakers or through the C speaker, and when they come through the C speaker the L+R ones are very low in volume. I've also managed to let the sound come out of all speakers but the C speaker is still the loudest and the L+R are very soft, the back L+R speakers you can hardly hear, and the subwoofer hardly outputs any bass at all, even when I turn the knob all the way. Before when I turned the knob even 1 millimeter the room would shake.

The input on my receive is set as HDD/MD and the sound field I selected was PLII Mus (L+R, C, SR+SL, SW and LFE).

I've mucked around a bit with the (Realtek) configuration too where I have the option to choose 2ch, 4ch, 6ch, 8ch, Dolby Digital 5.1 or Dolby PCM output. Furthermore there are side-options to select ProLogic IIx, Virtual Speaker and Dolby Digital Live. Tried several combinations but in all cases the sound is not what it should be. I know that when its done right all speakers should output quite loudly even when the volume knobs everywhere are only half-up. Now when I set my system to the maximum (software mediaplayer, windows volume, receiver) its not too loud at all and the subwoofer is virtually quiet even when tracks are played with a lot of bass.

Any help is greatly appreciated

Thanks already.