Especially the Descent and the Depth. Their new versions of these subs have higher wattage amplifiers as well and they are labeled the Descent "i" and the Depth "i". They are both really stellar performers the depth with it's tripple 8" drivers was able to deliver +/-3 db to 18 Hz.
The real issue with these subs is their pricing compared to all of the newer ID subs. They are not competitve at all with these subs and a lot of these ID subs will simply out perform them for a fraction of the cost. Now granted, a lot of them are no where near as attractive as the ML subs, that is for sure. I have heard the Descent many times and it can sound as if it wants to bring the house down, but so can all of the heavy hitters from SVS, Epik, ED, HSU, AV123, etc.
The ML subs (the Descent and Depth) are both really great for HT and for music. You could not go wrong purchasing either as long as you are ok with the extra money you will spend. The are astetically awesome looking in my opinion and are excellent performers.
The Grotto is a very good sub as well as it is servo controled but it will have no where near the output of the other two. And it's single driver design would be made mince-meat by the ID subs. It is really up there price wise compared to the ID subs and could not hang with them at all for HT. It is really great for music, and can do some justice for HT, but again for the price it just can not give you the "Performance per dollar" that the ID subs can.