I know Windows liked to turn off the back speekers on my sysytem every now and then for no reason and set it to a 2 speaker system. Depending on what version you have, it might only be mono anyways (like my TV Wonder VE I picked up for $30). I also ditched the patch cable for the sound and got a short one that used RCA cables instead. The interferance was pretty bad from the cheap cable. I also had to turn down the mic in on my SB Audigy so it matched the rest of the sound levels on my system. There is still no base, but it works OK. Make sure you download the latest drivers, Cable Guild Plus, and MMC 7.6 beta.
If the front speakers are working though it is likey the sound properties are not set right in Windows. Laad up Creative Labs AudoHQ and goto Speakers and make sure it is set to 4 or 5.1 speakers.
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