Thank you for the replies! I am using Windows XP w/SP3. The sound was working great but then it started getting goofy, but the timing was paper cut-like, and I couldn't remember exactly when it started.
I did update the drivers for my graphics card (ASUS EAH4850 series [Display adapter]) around the time the sound began to flake out, and when I went back to see what was included I realized that the update included sound drivers. I used the uninstall feature to remove all elements from ATI's Catalyst Control Center and other assorted goodies with the install. I reinstalled the graphics driver and unchecked the audio driver. Alas, the sound is still up and down.