my first suggestion for a good bass is to sound proof the front door, parcel shelf and boot area... that probably cost you around $300-400 depending on the material used..

listen to the sound after that and then upgrade your gear... btw, what sub are u running now?

for loud bass I found kicker CVR12 gives out tight and deep bass... good for RnB music. Other sub I've heard good for RnB is the Rockford T1 series. Basically if u want loud bass go for american designed subs... but this is from personal experience, others may say different..