Subwoofer for Wilson Cub

To all,

I am thinking of buying a Wilson Cub2 for my second hifi set. But as you know the Wilson Cub does not have a good bass. So I need to add a subwoofer.

Which subwoofer will fit the best. I mad already a selection:

1. Wilson Watch Dog. The best of course but at a price of 18000 euro in Europe (21500 US$) it cost almost as much as a Watt / Puppy.

2. Revel B15. This is a good sub and it is small. But will it work with the Cub.

3. Velodyne D15 or DD18. I heard this sub together with JM Lab Utopia and was not to impressed. A lot of bass but not so musical. Or was it setup wrong.

Please advise which sub will be the best choise.

Peter