Right now I have a Pinoeer BEH-2200 UB Head Unit going to a Sony XM-GTX6040 amplifier. I have some Sony XS-R5743 4-way speakers running through the front channel (via High Level Input), and a random 10" Kicker Subwoofer running through the Rear channel via RCA (my HU only has Rear RCA outputs). With all that said, Should I get 2 more speakers + amp and bridge the amps? or get a better subwoofer(s)? My budget is $300