set the switch to LPF which means low pass frequency..which will only allows the low notes to pass through the subs and the input sensitivity should be at about half or else the amp will pick up bumps in the road and every electrical thing in your car can create interference.. and for the bass boost turn it up about 1/2 to 3/4 of the way up a good way is to turn your head unit up with the bass boost all of the way down to a little louder than you would normally want them.. then turn up the bass boost unlit you hear the subs distorting a little and then turn your head unit back down to where you would normally play it and listen for distorting.. keep doing this until you get it perfectly the way you want it