I have had two of those though briefly. The subsonic filter, filters out frequencies below the Hz you select. It is used to eliminate frequencies below your box tuning or simply below 20 hz because we cannot hear less than that. Low pass filter, filters out frequencies below the selected frequency, keeps your sub from trying to produce midbass. Bass boost and Bass eq work in conjunction, the boost is the amount of dbs it will add at the frequency the bass eq is set at. I used mine to help punch out dbs at 40hz typically during comps as my box was tuned just below 40 and my truck loves it at 40hz. And if I remember correctly Q control is your cutoff frequency slope (typically 6db/octave, 12db/octave etc.). The narrower your Q is set, the stricter your slope is on your LPF setting, the wider the Q, the more liberal the slope is for your LPF setting. I dont really want to get into the whole db/octave explanation, but basically I hope the latter sums it up. As for the slave/master setting, leave it at master unless you are strapping amplifiers.
