Post is long because I tried to give as much detail as possible.
My audio system:
Creative Sound Blaster Live 5.1 audio card with 5.1 Surround Sound speakers
Software:
Media Player Classic v.6.4.9.1 (Rev 55)
K-Lite Codec Pack Full v.4.0.0
AC3Filter v.1.46 (installed with the K-Lite)
Before Reformat
Before I reformatted my PC and using the audio hardware and software above, when I played downloaded video files (avi, mpg) such as SMALLVILLE, the audio sounded like 5.1 (with voice/vocals/dialogue coming from center and front L and front R speakers).
This was also the case with playing DVD's on my PC.
Everything sounded perfect.
After Reformat
Now however, since PC was reformatted and software (above) was installed again, the sound from the downloaded files (especially the voice/vocals/dialogue) play only from front L & front R and rear L & rear R speakers.
AC3 filter does not come up when downloaded files are playing so I can't fiddle with it either.
Furthermore, with my DVD playback, the voice/vocals/dialogue and other sound effects are coming out very strong from my center speaker. The voice/vocals/dialogue are very low on the front L & front R speakers as well.

Under Control Panel, my sound card is set to 5.1 sound.
Under AC3 filter, my input is set 3/2 5.1 sound
Under media player classic/Playpack/Output/Directshow audio:
-I can either set it to Soundblaster live [which makes my downloaded files' audio sound LOUDER(but still not 5.1) and my DVD playpack sound LOWER (and a non-working center speaker)]
OR
-I can set it to Directsound or Nullaudio, ect [which makes my downloaded files' audio sound LOWER (but still not 5.1) and my DVD playpack sound LOUDER (and a WORKING and STONG center speaker as explained in "after reformat" section above)]
The sound just doesn't sound right anymore in either dowloaded files nor in DVD playback. How do i go back to the way things were before the reformat?
Thanks

Have you looked in Event Viewer for hardware or application errors ?