maxima bass 2005 system

Hello all, I'm looking to upgrade the GFs vehicle. It is a 2005 Nissan Maxima SE. We currently have a LOC, 4gauge(probably not true 4), 2 kicker 12s sealed(separate enclosures) powered by a jl 500/1 It is just not doing it for us, the bass is minimum especially after the dampening of the...