having speakers placed directly into the corners doesn't give me a lot of flexibility when dealing with room resonance. Also, the fixed 45 degree angle of the corner horns doesn't leave much room for flexibility either.

What happens if opt for the 7's and build an asymmetrical horn? Basically, taking the existing design on rotating the bass enclosure a few degrees while leaving the corner section at 45 degrees.

This is starting to look like quite an engineering challenge.