Sound working for some programs, but not others

I just recently moved and set up my PC again. The two speakers are plugged into a subwoofer and the black and green wires from the subwoofer are plugged in to the back of the desktop. I seem to recall there being other colored wires before I moved, but can't find them, and might just be getting confused.

At any rate, sound is working for some programs on my computer, but not others. For instance it seems to work fine for Windows Media Player - for both movies and music, both speakers work fine. Same for DosBox games, and other games I've tried.

However for Winamp, as well as Firefox and IE (for video sites I tested, like YouTube), sound doesn't work at all. I restarted my computer and have tried to check all mute and equalizer possibilities, but can't figure out what's going on.

What might be causing the inconsistent sound here?