no doubt the xxx will beat the w7's in spl, but sq they will be no where close (although the xxx is not BAD in quality at all, the w7 was made that well). I personally am not a brahma fan, good subs, but i think the w7 has the edde in sq again and almost identical in spl. Those XXX's need more power too. I would say if your going for quality go jl, loudness XXX. As for amps, dont use those jbls with sub awesome subs. Someong suggested the JL 1000x1...i would add Xtant's 1000x1 (amazing amp) and PPI's 1000x1, all great amps, whatever you buy, generally you pay a buck per watt for a quality amp (very general rule of thumb). I am still going to suggest that you downgrade to 2 subs, but thats just me. As for the 15 hz question, the human audiable range is 20hz - 20khz...although some people can hear a little below and above. Changes are you wont hear that at all, but you will feel it like mad //content.invisioncic.com/y282845/emoticons/smile.gif.1ebc41e1811405b213edfc4622c41e27.gif thats what being a bass thug is all about right?