16 x 12.5 x 8? Shouldn't be a problem for the 5's or 5A's. They seem to work very wall in medium-sized rooms like your own. In fact, I would say they work better than they do in larger rooms. personal opinion, obviously, but I think you'd be in good shape with that.
Just be sure to experiment with having the speakers against the long wall. Seems to come out better more often than not.
Just be sure to experiment with having the speakers against the long wall. Seems to come out better more often than not.