Yes, it really is that sub par, especially with a big open area. Your sub is underpowered as well as low quality. Like Bill said, Hsu is probably the value leader for subs but the
PB/PC2000s at SVS (scroll down a little) are priced pretty nice. I would probably nudge you toward a pair of those at minimum with a preference for a pair of
HSU VTF-3 MK5s. Price in the HSU link is for 2 of them.