I've used the QS4s & presently have the QS8s. Interestingly, in my room, my Audyssey 'heard' the low end of the QS4s as 80 HZ & it hears my QS8s as 90 Hz.

Due to the sporadic nature of surround content, I have noticed no difference in the performance of my system between the 2 models. IOW, the QS4s will work just fine unless your room is really large...

TAM