Some numbers on the JTR Captivator I posted earlier:
2011 JTR Captivator *<10% THD continuous*
119dB @ 15 Hz
120dB @ 20 Hz
121dB @ 25 Hz
122dB @ 31.5 Hz
123dB @ 40 Hz and above
At $1000/ea (minus amp) you could get four plus four behringer EP4000. Probably destroy your room while your at it and if four ported 18's can't, don't think much else will.