I have the Velodyne DD10, and use it in a less than ideal room (12 x12, opening to a small sunparlor). Its used for 2-channel only and it adds a layer of warmth and complexity my monitors were missing. The software is incredible and easy to use. It greatly reduced my room problems in the 40-60hz range, while still having a full, rich base sound.
The dd10 or dd12 is a great choice in a small sub.