Then you need to include the kitchenette in your room size calculations.
Boominess isn't simply a matter of sub output. Most of it has to do with sub quality, sub-placement, and the room itself. For example my family room has a bit of an odd shape and I had to install a pair of bass traps. I no longer have any boominess in that room, just tons of good clean bass on tap when the material calls for it.
The nice thing about big powerful subwoofers is that you can always turn down the sub's volume. Other than adding a second sub there is no way to turn up a too small sub past 100%.
It doesn't look like Wharfedale publishes detailed frequency response specs for that speaker (28-24k -6db) but I think I'd set them as small and set crossover at 60 or even 80hz.
BTW if you're in an apartment or condo you'll want to keep neighbors in mind when selecting a sub. For example I wouldn't want a rear base port hammering a shared wall and I would probably avoid down firing subs if I had somebody below me. I'd also plan on using a SubDude.