Sound Card Problems With WinAmp

I've got WinAmp 2.91 and it seems to have problems with my sound card or something. Becasue it doesn't output sound to my rear speakers, but when I play audio in Windows Media Player, it works perfectly fine. I remember having this same problem before I reinstalled windows and everything, and I did get it fixed, but I have absolutly no knowladge of how I did it. Any and all help is gladly accepted.

TIA,
~C.P.