EDIT: In Realtek HD Audio Manager, if I set the configuration to 5.1 Speaker and click "Speaker Fill", it plays music out of all but the "front left"-labeled speaker.
EDIT2: In the picture here, the arrow that I drew is pointing to the speaker that isn't working. When the test comes to that speaker, the sound comes out of the subwoofer, instead of the proper speaker
EDIT3: It seems that in the test, when the sound system isn't picking up a speaker, it plays the noise from the subwoofer. I plugged one of the speakers I knew was working into the front-left speaker port on the subwoofer, and it played through that speaker. However the when it tried to test the speaker port that didn't have a speaker in it, the sound came from the subwoofer.
EDIT4: I pulled a speaker from my old setup, and plugged it into the left-front port. The sound now comes out of that speaker like it should.
TL;DR: DoA speaker, replaced with another.
Edited by Mozzy, 26 August 2012 - 12:58 PM.