Headunit: Pioneer AVH-P2300DVD
Subwoofers: (2)15" RE Audio XXX(05 model)
Sub Box: Undecided..
Sub Amp: Crescendo bc3500
Speakers: 6.5" RE Audio XXX Components(soon to be 2nd pair in kick panels)
Speaker Amp: Hifonics HFi100.2(for now...)
Wiring: 2 runs of 1/0 throughout, XS Power battery in trunk,big 3 done, 270a alt, 1/0 accesories throughout
Deadner: 75sq ft AT 60mil, 20sq ft Alphadamp
Security: Crimestopper 2way alarm/remote start
Before you go spend over a grand on new woofers, I would look into how you blew a 300$ one. What amp was this powered by? I ran 3 stock 18 Q's off of 8000 watts with zero problems, and watt by watt others have claimed Fi to be the most abuse-proof woofers out there. Just a thought
Cone area on an 18 is about the same as 6 8's if I remember right, so probably won't be much more output out of them if any. The Q is more efficient as well, and you will be under powering those w7's.
I think if you get 2 15's or even another 18 and put them in a 6-7 cubic foot box tuned to 32hz you will be surprised what you can do with the right amp.
This is gonna sound snobby but I don't mean it to be, but at the level you are at you are probably right. It is much easier to set up a 2 12" setup. I think 6 8's is a little too much. Look for 2 12" subs with a low fs, high Xmax and a big motor. If you could find some TC ssounds 12's I think that would fit the bill, unmatched in low end output
Look for used older tc. Many say they make the best sounding woofers available. Tc3000's DESTROY w7's. I know first hand. I had my tc3k on 2500 watts against 2 12w7's off 2000 both ported and the tc beat it soundly in every category. Once you get one in your hands you realize why they are better.