Best way about it would be to get someone on the forum to build you a custom ported box, tuned to about 32-35hz, and you will notice a complete difference in your setup!
why would you just add 2 more if you already dont like how the 2 you have right now sound? This just doesnt make any sense to me, dont let people who clearly have a bias tell you what to get man, use your own mind, not theirs