Unless you have skill in metal work or access to such technology, I would be thinking of what you can do with wood working skills. You can build a rectangular box similar to the outside dimensions of the Mac box and brace it to strengthen the baffle. I have used multiple full shelf internal braces in similar wide face boxes.

I don't understand what wings would for you unless you are thinking of an open baffle application. If you go open baffle, you need to equalize a lot to cover the lower freq ranges plus add stereo woofers to cover the bass area. The NSBs are too small and inefficient (bass wise) to do much for you down low without a lot of dipole EQ. Maybe 34 NSBs per side will help but EQ will be needed to make the open baffle work.

By the way, you mentioned rounding the baffle edge for BSC. Rounding of the front baffle does nothing for BSC but does help baffle edge dispersion higher in frequency. With your active crossover the BSC you will have to be EQed (that is if you are using a vented or closed box). Of course no BSC for open baffle but dipole compensation will have to be done for good results.