musical small sub for B&W 805s's

I was thinking about movin gto floor standers but there are things that I like about my 805s's that i have not found anywhere else.
Has anyone had any good experience combining a small sub or two with 805s's? right now I have a 15" sub that leaves just too big a gap.
I like the imaging and upper end but want the punch that I hear with full rangers. Listened to the 804s, 802d's and vienna mozart grands so far. liked the viennas but would really like to find an 8 or 10 inch sub that i could pair with the speakers that I already have.
thx!