Hmm. The Chesky disc has a set of low freq only signals that rotate through the mains. When the low freq info *hits* a particular channel, there is a high freq beep through that channel. The idea is this: with all speakers small, the low freq content to the sub doesn't change, but where the "beeps" are does, so that you can make sure that the BM is working properly. I reckon that if I set all small, except mains to large, I should still get the beep in the center but the sub should fade away. I'll try this Thurs PM unless someone gets to it 1st...