Ken, I don't don't do that, but my immediate impression is that you'd have to set the center speaker to none in the main menu or set it to the minimum in the "Home" menu. No one-step process comes to mind now.
It appears that what you want is no center speaker when playing music, so my thought would be to set the DPLII Center Width to the widest setting, which would send nothing to the center speaker. Since that applies only to 2-channel source material, this wouldn't have any effect on the center speaker for 5.1 movie material.
