I came somewhat late to this combo but I can fully support more or less everything what Mark said.
I have tested a number of soundbars in the recent past, including Sony's HT-ZF9 (which sounds surprisingly bad to me given the overall positive reviews), Bose's ST300 (which has a serious HDMI bug and a sort of "Auto-Gain" function that cannot be disabled), Samsung's K950 (strangely balanced rear speaker levels, only correct in Atmos mode), plus some others.
I recently got a MS650 for a very low price that sits in the bedroom. I was surprised how good this thing sounds, even without a sub and especially for voices and music. So I have the MS750 a try for the living room and today I added the SWA-9000S rears (that I had already in use along with the MS650) and the SWA-W700 sub. And that sub really really makes a hell of a difference. With movies as well as with music, this set very clearly outperforms all other systems that I had here, including Samsung's K950. Yes, you do sacrifice Atmos, but it's exactly as Mark said (at least for me) - the advantage of Atmos can be used occasionally only, while the huge difference that this sub makes is present all the time.
One question I have: SWA-8500 and SWA-9000 - does anyone know if there are any other differences than the wireless dongle that is shipped with the SWA-9000? From what I can see, the speakers also also the base unit are absolutely identical. Since the SWA-W700 already comes with a wireless dongle, I am thinking about getting the (approx 50 bucks cheaper) SWA-8500, hoping that it will pair with the dongle from the SWA-W700 the same way as the SWA-9000 would and where I would have no need for the dongle that comes with it.