I also have a full B&W setup. Based on some auditions and reviews, I'll probably upgrade to something from HSU or SVS when money allows :frowning:. They both have offerings in your price range.
Axiom makes a sub I like for music listening; the EP350. It's ported on the front but they use a 'vortex' shaped port design that eliminates chuffing and noise. Uses a 12" aluminum cone with a 200 watt amp. Fairly natural sounding overall and not boomy whatsoever.