"Armor Bonus" is now Armor Bonus and Shield Bonus. Armor Enhancement Bonuses and Shield Enhancement Bonuses continue to stack... Now we just need to separate the "Enhancement Bonus" from Adamantite from the EB of magic, say by calling them a "Materials Bonus" and an "Enhancement Bonus". Of course, then, they're two separate bonuses, and the "Materials Bonus" will stack with the "Enhancement Bonus"... unless you make a special case of them, like saying that Masterwork and Enhancement Bonuses don't stack...