The Pre/Post switch on the GK MB112-II is described in the manual to allow you to switch the direct out signal between pre- and post-EQ. So, in pre-EQ mode, the equalizer will not affect the signal. In post-EQ mode, it will. However, the switch also places the signal before and after the Gain settings. Therefore, if you are in post-EQ mode, it will also be post-gain which means the amplifier will still send signal to the cabinet. Because there is no master volume on this unit, you cannot turn off the external sound and use the direct out silently when it is in post-EQ mode. If you want to use the direct out silently, you’ll have to switch to pre-EQ mode.