I agree with your thinking here.
I tend to agree that although they are great in certain rooms, yours might be a wee bit too large. I think this would be an issue with any diminutive speakers though.
Have you considered their Audition series? A pair of AS-F2's (or F1's for that matter if you know you're going for a sub) for the mains, The C1 center and a pair of B2's for the rear surrounds (or R1's if you want bipolar) won't set you back too much more $$.
But, I'd suggest a non Athena PS series sub. They are good in a smaller room but there are better available for a bit more, particularly in a room your size. Check out SVS, Hsu, Adiere, etc...
