try decreasing the crossover a bit. you will get more bass but it will also decrease the power handling capacity of your speaker

so you have gain to control the right amount of power going into the speaker
LP/HP & flat to control the crossover cut off (ie frequencies played by the speaker). It will still play the frequencies below or above the cross over points but at lower volumes. typically -6db or -12 db for hp, depending on the amp.

your amp has a variable crossover point. so by crossing over at a lower point, you are allowing the speaker to play lower frequencies with out the amp cutting them off. as i said before, this will reduce their power handling capacity because they are playing a much wider range of frequencies. hence you dont have a magical speaker playing everything in high end systems.

typically for 6in splits you can HP them at 60-80 hz
for 6X9's HP them around the same.

so play around with gain and cross over frequencies till you find a sweet spot.