I went to tweeter yesterday and did an in-store demo of the Grotto. (one of their smaller listening rooms) Now...in all fairness, what it did, it did pretty well. However, it was very localised. My attention kept getting drawn TOWARDS the sub. In addition the sub seemed weak.
Granted, the sub was along the side wall, and may be better in a corner. It also seemed like a good sub to run inline with each of the fronts. But I just couldn't imagine paying $1000 for it. In that price range, if you want to go with a smaller, sealed sub, you might want to look into the Definitive Tech Supercubes.