I have the combination BL3s + BL11 for about 3 months. The day I installed the BL11 (after some 3 years with the BL3S by themselves) my first reaction was of disappointment. I notice some difference but not much.
The fact, however, is that the more I listened to it the more I notice the huge subtle difference (if you know what I mean). it is subtle because the furniture doesn't start to rumble around the room and huge because it really complements the music and makes the sound much rounder and full.
I am very happy with the combination. You should have it tested at your home but bear in mind that the longer you listen the more you will like it.