Thank you, sir!
So in general it depends...;-) And you react in a very flexible way to the circumstances.
I take it you have no reservations to combine different kind of subwoofers (like horn and sealed designs) in one setup.
Did you do any designs having dedicated subwoofers only for the LFE channel, with another group of subwoofers handling ONLY the low-passed speaker signals (with your mentioned XO at ~80Hz)? Do you see any advantage in that concept compared to mixing...