cant make up my mind

[Curtis96olds 1]

im looking to upgrade from my previous setup which consisted of 2 AQ sdc2.5 15's and an AQ1200D, basically i want to get louder, but i have the same limited space i had before. the dimensions i have to work with are 47" wide, 15" deep, and 35" high. i will be using an AQ2200D to power this system. i mainly listen to decaf music or other rap/hiphop 90% of the time, other 10% is rock/metal. so a sub that likes to be tuned low is what im going after. my budget is 500-600 bucks tops. im just having a hard time making a decision because i want to make sure this setup will get louder... i dunno if i want 2 15's that can take more power, or a single 18, or a IA DP 21, or 4 12's... really any of those will fit into my area, but i dont know which, or which subs to go with for my budget while still getting louder then i was.