Subwoofer reccomendations for B&W 805S?

How do REL's newer models like the Brittania compare to some of these?

Thanks for the suggestions. Another question I have is right now I'm actually in a 13 x 14 1/2 room. I have them set up on the long wall (6ft away) and sit 6 feet back. When I move to the new 17x15 room I will be setting them up on the short wall (15ft) and will have the speakers about a 1/2 foot more off the wall, and will be sitting about a 1/2 feet more back (setting them up using the cardas method) Am I going to lose much volume going into the new larger room? I like to listen pretty loud at times. (85-90db) I hope my 805s will be good enough for the room. Right now they sound great in the 13 x 14 1/2ft room.

Also I am running them at 200wpc.

so would using two 10" subs be more than good enough for my 17x15 room?

Also, my neighbors house is pretty close to my house. What should I be looking for sub-wise if I don't want to disturb them? I have heard less distortion and cleaner bass is less disturbing and boomy. So would a REL sub such as the Stadium III be perfect? Or should I look at something else?

Does anyone where the crossover occurs for the 805s? Also if I was going Bob's route, what sort of "active" device would I need? I am new to all of this. What are the pitfalls of going this route? Also isn't bass at say 100hz still directional?