I don't know about the coliseum, but on the concert the distort and boost functions are all on the same knob. As you turn up the distortion, it turns down the boost (and vice versa).
And as far as the footswitch goes, the distort line has to be grounded to activate the distortion side, and the boost line has to be ungrounded to effect a boost. If you have them both grounded then it might appear that volume is reduced when the distort is on - or that you have more volume when distort is off.