Adding more bass: replace door speakers or add small sub?

'98 Ext Cab came with 4 Polk Audio db651s and a really sweet Alpine CDE-HD148BT. These things are shallow mount and the bass is just pitiful. Absolutely no low end and the mid range is also lacking. The other problems are that the tires on my truck are old, very hard and really loud (BFG KO A/T), so a lot of the fidelity of my system gets drowned out by road noise.

I'm curious about how to add some low end punch to my system without breaking the bank. I listen to a lot of hip hop, progressive house and electronic music that emphasizes low end.

I have a few options in mind that I was considering that y'all could point me in the right direction on or point me in a completely different direction.

Option a) add a Sound Ordinance 8" sub under seat along with the

$280 Alpine KTP-445A Head Unit Power Pack

Alpine KTP-445A power pack mini class D amp.

Option b) replace the db651s with something that can handle more bass and aren't so shallow and add the KTP-445A power pack to boost the clarity. If option B, which 6.5" speakers will carry some nice low end to complement the power pack?

Option c) just add the Sub.

Looking to keep this upgrade under $300ish if I can. What do you all think?

 

http://www.sonicelectronix.com/lp/quick-bass

 

http://www.sonicelectronix.com/search?keyword=Bass+package