Then 3/4's it is. Four drivers could be used, there would be a divider between sides. Literally like building two and gluing them together side by side. A bit over kill as you mentioned, but (4) SDX per cabinet would be quite a system.....Oh, and weigh a ton1/2" ply would require re-folding and you wouldn't be able to get away with not bracing it. Four drivers would require starting completely from scratch.
Just alot of dreaming before i get a new house....