Hello Robert

You could position the AVR and the 8 inch sub at their highest crossover points and then try (repeat: TRY) to smooth in the 12 inch at a lower crossover point.
Remember, you can adjust the upper limit of the subwoofer, but the lower extension is determined by the design of the sub.
There really is no reason to attempt this though, as the mains (L&R spks) should easily handle the upper bass region.
The EP500 should also quite handedly perform in this frequency region.
Enjoy your system!! \:\)

Those who have long enjoyed such privileges as we enjoy forget in time that men died to win them.