Hey Zapper,
My room is exactly the same size as yours and the 10" drivers and 150 watts of power that the MJ Ref 150 MK II's will provide, are more then enough. I also doubt that a 15" driver is fast enough to keep up with your Silverline Sonatas. I've owned B&W subs before and they are very good with movie soundtracks but when it comes to music, I've always found them lacking. Back a few years, before B&W got so heavy into subs, their dealers would push Rel subs as the perfect match. The MJ subs are made by some of the same engineers that worked at Rel before Rel started out sourcing to China........John