The x series never were and the first run had a lot of issues with the glue around the surrounds failing. Jacob made good on all of them but the point is that's the sort of thing that never happened with the older Z and NS series they built in house.
That said, the X is one of the least efficient subwoofers on the market right now. I don't care for Skar at all, but I'd give that a whirl before I'd run Sundown X.