I think you'll get much better boom for your buck if you venture outside the B&W family entirely. With a sub, you're playing the bottom octaves so there's not much reason to stay with the same brand as your speaker because timbre matching is a non-issue.
You don't mention your price point specifically, but I'd look into subs from HSU, SVS, and Outlaw for home theater. Rythmik and Velodyne might be worthy of a look as well.
You don't mention your price point specifically, but I'd look into subs from HSU, SVS, and Outlaw for home theater. Rythmik and Velodyne might be worthy of a look as well.