i'd focus more right now on front stage if i were u. a properly setup front stage will never make u feel like your missing rear fill.
and get a bigger 4 channel if it was me, or find a beastly 2 channel to just run some good mids off of.
i was able to do 144 playing Late night tip, out of my neon trunk on 2 type R's....on a hifonics bxi2006d. If i were to put subs forward and port forward and sealed it off, i bet i could of gotten more.