Ok so heres My Opinion sell all the current equipment you have and get as much towards new equipment . seeing as you dont have alot of electrical mods or budget heres the list :)
Amp : Mb Quart Onx1.1500 (true power ratings) 1000@2 Ohms x 1 channel
Also stable at 1 ohm at 1500 rms x 1 channel for future expansion
Sub : Sundown SA -15 Dual 4 ohm sub wired to a 2 ohm load for a real life 500-750 rms
Or a Obsidian audio Dual 4 ohm 15 wires for 2 ohms , 750-800 rms
Headunit : Upgrade to atleast a Pioneer with a pair of 4 volt Preouts ( rca connectors 1 for mids/highs amp , the other to the subwoofer amp ) and atleast a 5 band Equalizer for the cleaner sound all around . High pass filter optional but recommended.
Box: 3 routes here really, a high quality prefabricated box around 3.5-4 cubic feet in volume . Build a custom box (requires a good bit of reading up ) , search Craigslist for someone selling a custom box fitting your needs and that will fit in your car .
and of course, proper wiring,fusing, and all other safety goodies
My record is 1.5 miles from being heard to being seen ;)
Current : 2 15s 149.5@56hz 2k rms Previous Trunk box 1 18 ,146.4@43hz 3500rms,Sony 12s 145.6@63hz