You want gauntlets to be something besides a bonus to AC, but that is the system that D&D uses for armor! Unfortunately, what makes sense for a gauntlet to be some sort of parrying tool, as they so often were, is to give a small deflection, shield, or armor bonus to AC that doesn't stack as long as it isn't used as a weapon in that round. It is functionally exactly like a shield, but is instead a weapon. I'd say that there should be few ways to increase the AC bonus.
Alternatively, you could go a little more realistic: If you do not attack with the gauntlet on your turn, you can use the gauntlet as a a countermeasure using an attack of opportunity. When someone attacks you, you can expend an AoO to make an attack roll with the gauntlet, +1. If your attack roll is higher than the opponent's, you take half damage. Obviously, you can only expend one AoO per incoming attack.
Of course, that is how I think that all shields should work, with bucklers giving a +1, light shields giving a +2, heavy shields giving a +4, and tower sields giving a +6, with the added caveat that a tower shield converts the half damage taken to nonlethal (or you could say all shields do this, but the tower shield negates ALL dmamage on success). The present system for shields sucks slimy crack balls compared to reality.