My Sound Blaster Audigy 2 ZS has a stereo output jack labeled Center/Subwoofer. The left (white) channel is for the center speaker and the right (red) channel is for the sub. The center channel works just fine but I don't hear anything in the sub channel when playing either Bioshock or TF2, even when I have "5.1" selected in the audio options.
I'm curious if anyone else has a 5.1 setup similar to mine and, if so, if their sub if working in either of these games. Note that I'm running Vista (on that hard drive, at least) and when I use the built-in test utility where you click on each speaker to hear it, I do hear bass from the sub when I click it's icon. So this makes me wonder if these games truly support 5.1 (the .1 is the sub) or if they're just 5 channel (center, front left, front right, rear left, rear right).