I think what you're alluding to about the specs is the actually frequency response of the box. That usually doesn't reflect what you need to do as far as EQ. The only way to "flatten out" the box properly is to use an FFT analyzer like SMAART to figure out those settings rather than rely on the printed specs. You may find too that trying to flatten the response may not help the box sound better. I'm not aware of anyone doing any real work to really fine tune those boxes. They're pretty low end and probably not worth the fuss. That said, it could be a learning project for ya.
As far as crossover point goes, those boxes don't go very low. It depends on the volume you will be running them at IMHO. If you want the most output with the least amount of distortion, you would want to high pass them above 100Hz, something like the 120-150Hz range @ 24dB/octave. For lower volume, you could run them lower, say down around 90-100Hz for smoother top to subwoofer transition.
