I owned the Monitor Audio FB212 and now own the Martin Logan Descent. The Descent is exllent and the fastes sub I've ever owned. The Monitor Audio FB212 was great with Video and packs an awesome punch. It's not quit as quick as the Martin Logan nor as musical but the FB212 had more power & punch. The Depth is smaller than the Descent so imagine it's got less punch & power but I bet it's very quick. So your choice depends on what is more important to you.
