Bob,
Believe me, even with a crossover of 80hz, there is still a LOT OF KILLER base coming from your mains. 80hz is very low. Also, it does not just CUT OFF at 80, there is actually a gradual slope or blend during the transition.
The sub having a larger driver and built in amp will do a much better job with those lower frequencies than the small drivers on your center, surround, and mains. Yes the specs show the 60's and 80's go that low, however, they just can't move as much air as the larger sub driver.
This is why I recommend in your other thread a bigger sub for that huge space.
Besides, THX and others recommend 80hz for a crossover, which matches up with how the movie soundtracks are designed.
