I recently added a DSW sub to my main system. It definitely improves the low end response of my DSP5200SE based system. It adds a lot more presence to the room.
The problem I wanted to address is that (previously) the 5200s sounded great but didn't really "energize" the room. I live in a loft-style apartment with a very large room that is my living room, dining room, and kitchen. It's about 20' x 30' with high ceilings (11'). I.e. > 6000 cu. ft. The 5200s alone can play loudly in this room, but not with a lot of bass that is felt, rather than heard.
In addition, the Sonos SUB attached to my Dynaudio Contour 1.3SEs (still set up in the same room), routinely pumped out more bass. The Sonos SUB, as anyone who has one will attest to, pumps out a surprising amount of quality bass.
The DSW easily addressed this problem. I don't know if it has the "low-end thump" that some people may require, but in my >6000 cu. ft. room, it has plenty of thump for my purposes. Furthermore, it frees up the 5200s a bit so that the combination sounds remarkable and can achieve very loud listening levels in this room.