Turn the treble and bass knobs to 12 o'clock and turn the gain/volume control counterclockwise so that it is at its most minimal level.
Put a CD into the stereo system. Preferably it is a CD that you are familiar with and that has a clean recording quality. Push play and slowly turn the volume up to a moderate level. Adjust the treble and bass controls to where they sound best. Continue increasing the volume by turning the gain knob until the sound begins to sound distorted. Back the gain knob off until the distortion clears up.
Turn the bass boost to the on position. Push the play button again. Adjust the variable knob on the bass boost until you find the right amount of bass with no distortion. The bass boost increases the overall output of the low frequencies. This makes it easier for the subwoofers to be heard. The end result is deeper bottom sound with no distortion.