Opinions about sub for this system appreciated

Thanks for getting me started in a couple of good directions. I had thought about Rel already (opinion about a specific model appreciated), but had not considered JL Audio (definitely on my radar after checking out reviews, though).
Thanks much. Looks like either of those mentioned will be sufficiently powered by the 200W of the MA6900. Are there other considerations I should be looking at?

REL B3 is fairly easy to integrate and would be a good size for your room. I dont care for the new 'R' series.

Docdocgs,

I used to own the Kef 201s, had them in small as well as larger room. I used a Velodyne SPL-1200R sub. I was never really satisfied with the integration though, my feeling was that the Velodyne was too slow. I would aim for a 10" sub and my first choice would be the JL Audio Fathom F110.