I also get about double the bass in 5-channel stereo. My speakers are all set to small and crossed over at 80Hz. I recall a post a few months ago that noted why there was increased bass. Hopefully, the Gunslinger (Gonk?) that figured it out will let us know why you get so much more bass in 5-channel stereo. It is a little annoying but I adjust my sub down on the rare occasion I listen to music in this mode.