The Velodyne DD18 has been gathering good reviews and it's a great sub. It's very powerful and has built-in digital EQ. I don't know very much about the B&W only.
Now the Velodyne is very big sub and that may not fit into your room.
Unless you are interested in very high SPL at low frequencies, you should be able to find a cheaper sub that does a great job too, especially if you're mainly interested in watching movies rather than listening to music (2-channel). If you haven't done so, try the DD18 in a calibrated home theater to really **feel** its power
If I were you, I would rather buy 2 smaller/cheaper subwoofers that would integrate better and give a better bass response in the room than one huge sub. But that's my opinion.
For instance, SVS makes great subs with low prices (compared to many others). Their tubes are easy to place too. Now I have to admit that they have a special shape that does not fit everybody... Velodyne has some smaller models too.
Anyway, I strongly recommend that your do your best to try them before you buy anything. The best option would be to borrow your preferred choices and try them with your system, in your room. A/B testing is a very good way to find out what your really like.
As for Audyssey on Denon receivers: I have experienced that I always have to setup the subwoofer level a few dB higher after the calibration is completed. Looks like many people do the same. Maybe we like bass higher than the Denon guys do
Good luck !