dont listen to these fools who have never herd of any of this stuff. first off dont touch audiobahn with a 10 foot pole, if a company has to make its product look good and its still cheap then they must save money somewhere else. audiobahn = shit. people are gonna say thats not true but all they have herd is rockford, kicker, pioneer, ect which are all low end brands and all sound really really crappy compared to the stuff you listed when paried with a good amp. those subs you listed are some of the best you can buy. all will have excelent sq and a ton of spl too.
the xxx will have the most spl and the brahma will be close behind. but the elemental is no slouch either.
e12a will have the best sq with the brahma close behind, followed by the xxx.
the e12a will do everything the xxx will do but better, personally i would take the e12a or the brahma over the xxx.
you will get better info and reponses here:
mostly for elemental designs questions,
go to the subwoofer solutions and ask and you will get tons of good info,
here is another great resource,
there is a ton of info about these subs on sound domain just do a search.
another good sub that is in the same catagory as the others is the Magnum D2.