I tried everything at 60hz, and to me 80hz just sounds better. So the 7ii's and 64ii are crossed at 80hz, with the dual subs.
In 2 channel music though from say my Ipod, i run the 7ii's in pure without subs, and they thump in a way it makes you smile. It really sounds good, but I have a beast amp too. For HT, with large subs, I think 80hz is just a better move. Let those multiple drivers on the fronts and center handle everything from 80hz on up and let the subs focus on 16-80hz.