the JL W6 would work..
if u are going to spend $400 for both subs, i would get an Image Dynamics IDMAX. the sound quality surpasses the W6 and it moves a lot of air. the most cone area in its class combined with 24.9mm of xmax (w6 has about 13mm). it would take about 2 12" W6 to equal the displacement of 1 12" idmax.
the idmax will take 2.0 cubic feet (if u can squeeze 2.3 cubes..port the box..u won't be dissappointed). the output is very good. a single one of these in a ported box with enough power would be damn loud.