I agree with swerveddy. The Abyss is incredible. And the Dynamo is not far behind. I have long searched for a very musical sub that also had very high output for dynamics in music and for HT as well. I have listened to many of the commercial subs out there, with little concern for price. I actually found that price does not necessarily correlate to sound quality with subs.
My criteria for a sub is solid response in the lowest octave, ability to blend seamlessly with mains, low distortion, accuracy, articulation, and power.
The Abyss is my current reference standard for meeting or exceeding all my criteria while also representing great value. It is the most musical sub I have heard, and adds a transparent, almost ethereal presence to the music. The articulation is wonderful, and it effortlessly tracked the most complex bass material I could throw at it. I played a variety of music of all genres and the Abyss was equally adept with all. It was never boomy at all. But what really surprised me was when the depth charge scene was played on HT, how visceral the impacts were, and how they were felt in my chest. It was truly remarkable how at ease the sub was with such a variety of material. The room I listened in was about 16 by 20, with a 10' ceiling and a double door opening leading to the main showroom. This sub just made me smile. The salesman told me they had just recently got the Abyss in and he hadn't had a chance to stress it like I did, and he agreed that the Abyss seemed to handle every type of material exceptionally well.
Nearly as surprising was the Dynamo. The sound character is essentially the same as the Abyss, with the output being the only diffence I could discern. I heard the Dynamo in a room even longer than the room with the Abyss, but with a ceiling about a foot lower. I compared the ML to many known and reputable subs, but the salesman noted that hands down it was the most musical in the room. The only sub that I thought came close in sound quality was a Velodyne, but I was always aware of the Velodynes position, where with the ML Dynamo is sounded as though the sound was coming only from the mains. For smaller rooms if you want the most musical and seamless sub for around the mid-$1k price point, I haven't found anything close to this subs performance. Similarly, I think you will find the Abyss an exceptional value among its peers at around the $1k price point. And both have a high WAF since they are remarkably small for their output, and also immacualtely finished. Further, both had a design where you could swap the mount and the grille and this allows you to use the sub in a front-firing or down firing configuration according to what works best in your room.
The only subs that I have found that have a similar musical purity are the JL Audio F112 and F113 which I auditioned the same day. They have a similar seamless, transparent purity, and musicality, but with substantially more output. However, the F112 is about three times the Dynamo's price, and the F113 is roughly three times the Abyss' price. So the JL's are a reference standard at this point to me from what I have heard, irrespective of price, and would be a great no-compromise choice for those who need extreme SPL or have large rooms. But I think most people would find the ML's would give up nothing, in all but the extreme applications, in sound quality and represent what I think is clearly the best value out there right now for the music lover.
Hope this helps with your decision.