As I mentioned earlier I have a phase difference when switching between stereo (with sub) and 5.1 (with of course sub).

The difference I hear between in phase and out of phase is the virtual positioning of the sound is centered where it should be, when the speakers and subwoofer are in phase. But the virtual positioning moves away from being centered and sounds just plain wrong, when the subwoofer is out of phase with the speakers. YMMV.

Will