When I was searching for a small sealed sub with a $1200 budget, I ordered the X-Ref 12 so I could compare it to others that I purchased/borrowed from a local high end audio store named Gramaphone. I knew Emotiva had a 30 day return policy so I didn't mind having to pay the $35 return shipping if I didn't like it. I compared it to many subs, some of which cost 4 times the price. The cheapest one being twice the price. Im not going to name any names but the X-Ref trumped all but one. Once I turned it on zoned it in and loaded some music, I was extremely surprised to hear that much noise coming from such a small enclosure. After playing around with the PEQ, I was sold as it allowed me to really dial it in. The only sub I thought performed better than it was one that cost $2500. It was noticeable but not worth the extra $1800.
In the end, since my budget was $1200, I purchased two X-Ref 12's and never looked back. I dont understand how I ever even made it will one sub prior to this purchase. Two subs fill out the sound so damn nicely. Its probably the best investment I've ever made to improve my HT.
A guy over in the AVS forums just got a X-Ref 12 to compare it to his 15" DIY and said he is selling the DIY and keeping the X-Ref. He said the smaller X-Ref not sounded nicer but it also had more output.
Before you make your final decision, I would wait on the Audioholics review as I think a lot of people will be very surprised. Someone in the BluRay forums said he exchanged email with one of the guys from Audioholics and they told him they are going to name it the best sealed sub under $700 and that it performs as good or better than some subs that cost 3 times that.