Run your HU with Sub System 1... its somewhere in setup. This way your subs volume is independent from the rest of the car, enabling you to basically have your speakers in the car at around 10 volume, or wherever it doesnt distort, and your sub to be louder. If that doesnt work, try just fading the volume towards the rear (if distorting speakers are in front).to be honest i have no idea....about the HP/LP...i have the 9857...bass is a -4...treble is at +7 and sub is at 10/15...ive never messed with the bass center frequency or the bass band with or treble center freq or BBE
Run your HU with Sub System 1... its somewhere in setup. This way your subs volume is independent from the rest of the car, enabling you to basically have your speakers in the car at around 10 volume, or wherever it doesnt distort, and your sub to be louder. If that doesnt work, try just fading the volume towards the rear (if distorting speakers are in front).
Or just get new speakers, but if you just tweak some things here and there you can do whatever you want.