I'm not familiar with your Paradigm sub... but Paradigm is a decent manufacturer and most manufacturers of reasonable quality subs don't intentionally make them boomy. Before ripping into it... or upgrading... you might want to experiment with the following:
Turn it down. Make sure it's set to proper reference level relative to the rest of the system.
Lower the crossover frequency. "Boom" is normally associated with 80-120Hz material. Lowering the crossover to 50-80Hz will often help. Just make sure your mains are up to it.
Find a different room location. This it the most likely cause. Rooms have a huge effect on frequency response in the 20-100Hz region. With modest equipment: some test tones (from a CD or PC program) and a $40. Radio Shack (analog) sound level meter, you can usually pinpoint the problem... and adjusting sub and/or listener placement will correct it.
If those don't help, try stuffing the port(assuming it has one) with a loose rag or sock, and if you're into modding, open the sub up and line it with more polyfill.
I was gonna reply earlier but the forum was down just now.
anyway, while I haven't any personal experience, many Sony SA40WM users have gotten very good results with the polyfill mod. Bass is usually tighter and more controlled. It should work on any sub as well.
I would try some of the information Dave was nice enough to provide, "first".
Opening the sub and stuffing it, being carefull not to block the port or getting it into the woofers magnet and basket ~{will change the subs sound to an extent}~. Will it fix your problem, maybe, maybe not!
Placement of you and the sub, along with the rooms interaction on it's frequencys play a big roll in the subs sound. I'd recommend as Dave has, try to work more on placment, output, and room interaction first before tearing into the sub.
Stephen, There are two ways to go about sub placement: Mathematical room mode modeling or trial and error. For the former approach, you might start with this thread from the DIY section of this forum. For the latter, one trick is to place the sub where the listener usually is (maybe set it in your chair)... and move around the room to see where you find the best bass balance. This will be the best place to locate the sub.
As a general rule of thumb, corner placement yields the most "room reinforcement" which can be bad (read: boomy) if several upper bass modes are coincident. At the other extreme is placement out in the room away from walls. This will tend to produce the least "boom" but may result in overall thin bass. Placement along a wall is somewhere between these extremes.
One popular solution with the enthusiasts is to place the sub in a corner (to take advantage of room reinforcement -both good and bad) and then flatten out the frequency response humps with a parametric equalizer, like the Behringer Feedback Destroyer (BFD).