If you select a sub you can set it to be an effect sub by modifying the "mode" This should toggle through pileon, inhibitive, and effect. Once you have it set as an effect sub it will only store effect data for the channels you record into it.
In blind you can select the channels you want and apply an effect.
In live you can select the channels apply the effect and record the sub.
The handle of the sub then becomes the size/intensity of the effect. This depends on what kind of effect you are using. The bump button turns the effect on and off.
