snakeyes
The short version of the answer: I love that thing. Completely disses the replaced Klipsch 10" sub.
The longer version of the answer is along the lines of making sure an upgrade is an audible upgrade and not a paper tiger. I had a free money back return period, so even though I couldn't listen in advance (they were brand new at the time and you couldn't find them anywhere) I was willing to take the chance. For me, the Monolith kicked the Klipsch sub to the curb in the first 10 minutes.
I believe
@shadyJ was working on an evaluation of the subs at the time and though he didn't spill any beans on the details, he did nod his head approvingly when I said I was going to jump on them the day they became available. The Monolith sub is built like a tank, looks fantastic, and it does what the best subs should do. It delivers the lower register under control and disappears in the room completely.
My other choices at the time were the Hsu and the SVS subs. I'm sure they would have been fantastic as well. Those of you who chose them chose well I'm sure. I simply had an itch to try out the Monolith and they were a homerun right along with the Songtowers.