here's what I would do:
Obviously, a BL is a great woofer. It'll get muchhhhh louder than your w6's sub for sub, but there's no way ONE bl is going to beat THREE w6's.
If you only have 1000 watts and limited mounting depth, i'd get two 10" Incriminator Lethal Injections (or some other efficient sub good off 500/each). Even though a BL will be significantly louder than the LI's, having two of them will surely get them louder than a single bl.