Your advice Please

Hello to all, yes i am new to this forum but not so much the stereo world. Anywayz here what i have, a 2004 ext. cab silverado. I recently bought a sealed downfire xscorpion box to go under the rear seat. I went with 2 12 jl 12w3v3's 4ohm with a memphis mcd1000 Mids are all Infinity front door is 63.9i and rear door is 462.9cfp and have a Memphis pr4.50, and the headunit is a kenwood ddx712. Got it all installed and i thought it sounded good but i thought it could be a lot better. so this is where i need some input

I am either going to raise the rear seat about an inch and make the box deeper and go with 2 jl 12w6v2's and put around 550 each to them or i am going to buy this box http://www.soundoffaudio.com/item.cfm/id/2252 and go with 4 10's they would also be 10w6v2's, i would have to get one more mcd1000 amp but well worth it to me if it sounds awesome


Input please and sorry for such the long post.