so i have 2012 f150 harleydavidson with sony system.

i rescently picked out a system for my sons avalanche and for what we did , i think it sounds really good, much better than my f150. not a screamer, but a very nice balance sound.

kenwood head unit with gps, stock bose speakers, rockford/fosgate mono 400 watt amp (around $300) running a shallow mount jl 12" sub. ( i got the first one crutchfield sold) $349.00. had a local shop install and make a box to fit under the back seat.

so first is the 400 watt rockford and jl 12" a good addition to the rest of the sony system? something better out there?

is the thing under the back seat a sub and an amp or just a sub, do i have it removed when i add the aftermartket amp and sub.