I have heard the Grotto and let me say it was amazing! It was not as low as my HSU for movies but much better for music! I think that unless you really need bear belly lows, this is the sub to get! I am thinking of selling my Hsu now since I listen to 90% music!
The quality of the finish is incredible and can be adjusted much better than the Hsu for all rooms. Let me say that there is lots of bass for movies so don't think that my comment is denying that only that it is a little less. I liked the compact design and for a sub weighing only 45 pounds, it can really hold its own without even breaking a sweat. I pushed it very hard and it never once went into protection mode whereas my Hsu would at the same levels!
Martin Logan is an incredible speaker company and matching this sub with their electrostatics was an experience I will soon not forget!
