Great minds...
You know, I don't have any experience with XBL^2 subs but I would imagine they perform similarly to LMS drivers with regards to nearly non-existent distortion, you often hear people describing them as sounding different as dkdub noted in your thread. Some people just can't get used to that lack of distortion since the only reference they've had up until that point was with inferior drivers. It's like the day you find out Santa doesn't exist, it just doesn't sound right but it's the truth. Love my LMS drivers.