I don't think we need to refit the Stingray design to have 6 cannons. They would mostly be there for better firing arcs. And as stated when we first designed them, the Stingray is nimble enough that keeping an enemy within its firing arc shouldn't be difficult and any opponent that can stay out of it isn't something the Stingray should be tangling with in the first place.
This will be even more of the case with the improved engines.
That may not be the case if @Sayle does the same phaser layout diagram as was done for the NX. Since that changed the firepower for the NX.
Edit: whoops! Forgot to insert the quote!