Just to clarify, I can't turn off my front left or front right. But I do have those 2 speakers on a separate amp so I can turn the volume down to zero.On my system if I turn off all speakers except center I can hear this weak, pathetic music signal that was created for the sacd's center channel.
This is also the case with my rears. They are on a separate amp as well and the center is on another separate amp. So it's pretty easy for me to leave all speakers on in the speaker configuration menu and then just turn down the fronts and rears to zero so that I can only hear the center. Sorry... wasn't clear about this before.