The H.P.M.S. allows you to control highpass LR independently, so used in my MS-processor (included like some other compatible tools) it is a bass2mono-device

The principle is simply removing S information on the bass signal or better the other way round: removing bass signal on the S path.
USE RIGHT KNOB TO REMOVE BASS IN THE S-SIGNAL (when insertet in my MS-processor).
H.P.M.S. 1-4 use different filters.