As I said, with the LS50 the bass registers fall a little bit short. Both, in regard to tonality and, sadly, in regard to available clean level. The deficiencies contaminate midrange and even treble. See the review on this board, elsewhere and many comments. There is one site that offers a binaural listening test in comparison to some, actually, huge speaker pair. I can't support the authors conclusion, though. My personal experience is as said, sadly.
So, if you want to go for the LS50, which is a sane decision IMHO, it might be a good plan to compliment the LS50s, each, with a bass speaker that would take over the registers the LS50 cannot deliver too well. These should hence be active at about 200Hz and down which simply rules out some (a) single (b) subwoofer.
Btw., this isn't new. Somebody on the internet offers such a solution for another speaker. A dedicated real bass namely to serve as a 'stand' for the mini speaker. Only I can't remember any name.
Hope this hint helps nevertheless.