Hi,
I have recently added a DSW to my system which is similar to yours (DSP5000s rather than DSP5200s). Before I added the DSW, I was happy with the sound playing music, but wanted a bit of extra bass when watching movies. I was surprised by how much adding the DSW improved the music sound.
I have now set it up so that it is running during music playback too. It took a little bit of setting up, but it does integrate smoothly with the DSP5000s and doesn't sound like an 'add on'.
I did look at (rather than hear) a B&W DB1 but the footprint was too large for my room. Although still fairly big, the DSW doesn't make too much of a visual impact. I chose mine to be white to match my walls

I'd definitely recommend a listen.
Oh and one should be enough. When calibrating it, I was able to get the entire house to vibrate
