Home Theater Newbie question --

I am using a pair of B&W CDM 7NTs and will eventually get surrounds and a center speaker. In the meantime I'm using a pair of ADC 303AX's for surrounds and a KLH 17 for the center. Not great, but the old speakers, particularly the ADCs, are pretty good bookshelf speakers.

I have seen some discussion to the effect that, when you introduce a sub you set the front speakers to "Small," even if they are floor-standing. I assume that's to take the bass load off them and put it on the sub. But I'm already getting pretty good bsss from the B&Ws. In a small room, 11 X 17 with 9ft ceiling, will it be overkill to add a sub, even a small one?

Thanks, Bob