Dell XPS 410, sigmatel high definition audio codec, 6 speakers.
Like many others, I used to have the audio hiccup playing wma files with this configuration. I could either have the hiccup or eliminate it by disabling audio enhancements, which meant only two speakers played. Then, after many months I managed to find a sigmatel driver that fixed the problem. I don't know which one it was.
I recently noticed that I'm back to two speakers again. I've just updated to the latest sigmatel hidef audio codec driver (6.10.5866), but this hasn't solved the problem. One of the auto updates must have overwritten the driver that worked.