I am just speculating but with that kind of separation and the nature of cinema dialog, a center channel will serve you well, as might a subwoofer.
I am a dedicated 2 channel person for music and don't own a home theater system, but in your case for movie dialog I would buy an absolutely and fairly substantial center channel. It should easily be the equivalent of your front mains, which I am guessing are going to be very high caliber gear.
I am a dedicated 2 channel person for music and don't own a home theater system, but in your case for movie dialog I would buy an absolutely and fairly substantial center channel. It should easily be the equivalent of your front mains, which I am guessing are going to be very high caliber gear.