Id go two opposing each other as that will be the only way to keep the box inert. The other way yields itself to box vibrations.
To clarify, opposing does keep the box from dancing, as there are equal but opposite forces to prevent that issue. Opposing per se doesn't do anything to stop vibration of the box panels, though the smaller baffle/back that opposing allows helps in that regard. But I'd still go with all separate boxes, for the better placement options that allows.