So have Brian Ding send you one Rythmik, and see if it's boomy. But here's something you need to be told: if you hear boomy sound from a sub in your room, the boom is more likely to be a result of the interaction of the room and the bass frequencies you're pumping into it, not the sub itself. How are you going to know what is the cause of the boom?
I think you need to buy a sub from a dealer who can help you with placement and other integration issues. Subs are tricky, and it sounds like you don't have the experience to do it yourself, whether the sub is a REL, a Rythmik, an HSU, an SVS, or any other make. No offense, Larry!