Sub to match B&W Sig. 805

I'm using a HT system with sig. 805 fronts, htm 1, and n805 for surround. I am currently using a hsu vtf 2 but would like you input on other recs. I prefer smaller size as I'm in an apartment. Additionally, anyone familiar with the s805, what crossover freq. do you recommend??

Thanks

JWH

System:
B&W Signature 805
B&W Htm 1
B&W Nautilus 805
HSU vtf-2
Meridian 568
Meridian 508.24
Audioquest cables