Funny how on other sites Sundown can do no wrong. If people can not see that then you might as well be blind. There was obviously enough people who didn't like the sound that Jake came out with an explanation of its sound so people would settle down. Take it as you will. I gave the x-12 4 boxes for it to show me something and didn't like any of them. It was muddy. Some may like that sound and I am not saying the sub is bad. I will however voice my opinion that if the subs mentioned in the op are the options then the x is at the bottom of the list. If you run the specs of the X and the Flatlyne for example, the X should be even more to my liking of low end extension. Put them in the boxes though and the Flatlyne will walk all over it in quality of sound generated.