Sub to use with B&W N804

I would like recommendations for a sub (>$700) to use with my B&W N804 and it would be nice to get the finish (natural cherry) to somewhat match. Anyone have experience with Polk Audio subs?
The REL Strata III is a very good match sonically with your speakers,, and no, i dont recommend using a Polk.
I now have upgraded to a N 800 that is a bit outside your apparent price range,, The REL will do VERY nicely however!