I stopped by an estate sale over the weekend and was lucky to find a clean Bowers & Wilkins ASW600 subwoofer for sale for $110. I grabbed it and headed home immediately.
Plugged into my HT system in place of the current Polk PSW10, I was immediately surprised at the difference in bass. The B&W bass is much much tighter, perhaps attributable to its sealed enclosure. In contrast, the Polk sounds much less composed, almost flatter. Both can put out equally low tones but it was much easier to integrate the B&W into the left and right speakers, especially for music - it seemed to disappear seamlessly into my BA-200s. It's very competent with movies as well. I always had a problem integrating the PSW10 into the L and R speakers for music - I could always hear the Polk. This seems to do the trick.
My Polk has moved upstairs to my bedroom rig, which consists of a Lepai 2020+ amp driving two B&W DM601s in support of the TV. It's doing a good job in that environment and since we listen at much lower levels there it integrates a little better with the B&W monitors.