Sorry you have taken lpf off, so xovers will not be working, lpf hpf decide which way the xovers work. you need the lpf, if i have misuderstood yourstatment and lpf is on, you have the amp cutting off from 50 up, and with a car your size (cabin gain ect) the peak freq would be from 55-60 ish maybe up more, so it will appear quiter, and your fronts will not be able to play (well if at all) down to 50 hz. Try rasing you lpf on your amp to 85 or 90, put everything to flat, and reset your gains (are you setting them by guess or properly?)
and try turning off ALL eq settings on the hu, no filters nothing.
and if the boxes are sealed sub will fade off allot more toward 40hz (hence why most ported boxes are tunned to 30-40hz range (street bass ))
Also who made the boxes? it could be that they arent sealed properly.
As for upgrading you equpminet, yes that will impove things,( but much sure the subs are in and set up first before you make any desisions to change.) the jls will drop much more (being 15s) but will be slower than ther counterpart 10s. it depends if your looking for quality or sheer volume or a bit of both in terms of subs (and amps) and how much your willing to spend on upgrades
HTH
rorrie