Best answer as chosen by user frigginlasers: Bob here.
I am not an expert on this setup but my suspicions is that the PS3 is outputting better than stereo. There are deep and long discussions about pass through of HD audio so I'll spare you that and move to the usual.
Try setting the PS3 to output stereo, pcm and such.
If I wanted more than that I find myself, most of the time running an audio connection from the PS3 or other source directly to the sound system.