I dont have any good answers, but a preference or two.Are you suggesting that properly fan braced mohagony cabinet with a rosewood back and spruce top would be bad sounding? :)
Be fun to make up some smallish units for fun and measure them.
I dont work with MDF anymore. I never liked it and used it beacuse it was good for veneering. well, it just plain suck most other times!
I do all veneer work over birch ply now.
Ther's more to be said for a 'tuned' cabinet than one made from 4 inches of concrete?
Bill