Clipmax is a hard / brickwall clipper.
Use Pre Gain to tame the signal before it hits the ceiling, or to boost right into it.
Set a ceiling value to cut off anything that would peak above it. The more the little LED to the right of the ceiling knob flickers, the more clipping is happening.
Auto engages automatic make-up gain calculation. This doesn't just boost everything up to the max, it tries to maintain a fairly natural volume level similar to the un-clipped source.
Use Post Gain to adjust the volume after the clipping stage and auto make-up gain. Be careful how far you boost this...