Losing the center channel when using 4.1 speakers

[Sinorm]

I have a video with a 5.1 ogg vorbis audio track, and all the sound works great, except the middle channel isn't playing at all. I have played with various options trying to fix this without luck.

I am using an Audigy 2 Platnium sound card, the video is an OGM file with divx and ogg codecs being used. For what it matters, I am actually using a 4.0 setup, with the bass being distributed across my speakers.