Something has screwed up my surround sound

[cholerajojo]

I had 5.1 surround sound working until today via alsa with the AC97 codec. I verified it regularly with that handy-dandy avi file (the "front left, front right, center..." one -- it was recommended on these forums). I did an emerge -u world today, and all of a sudden, I am not getting any surround sound. The only thing that was upgraded was qt. When I play the avi file, I only get sound from my front left and front right speakers. If I set the xine parameters to play in 2.1 stereo, I get sound from all the speakers, but it is just the sound from front left being mixed into the center and the rear left, and the sound from the front right being mixed into the center and rear right. In other words, it is not true 5.1 surround. Anyone have any idea of what is going on here?