Check the crossover settings before you do anything. It just shouldn't sound boomy unless there is too much overlap or some room resonance issues involved. If you have them yeah go for the SMS-1.

First though, do you have an SPL meter (Radio Shack) and a frequency response test disk?

http://www.genelecusa.com/ht/support/testsignal.php

Try this first, the sub you have is an excellent one.