allright time for my input ont he 9515f's.
depends on what you're going for,
if you want SPL....give each one about 3-4 cubes after displacement each.
if you want some big boom, 5-6 cubes after displacement...
and if you want just insanely low crap, 6-7 cubes.
buuuuut....if you go for 6-7 cubes dont throw more than 2kw to each one because they wont last long in a box that size with that power...
personally i enjoy 5 cubes after displacement per sub, which is what mine are in now, peaking @ 35hz...its loud, and plays as low as i want it to with no problems. how much power do you plan on givin?