Redirecting Enrage Damage
The Enrage triggered ability only triggers once.

An instruction like "[This card] deals 2 damage to each creature" deals all of its damage simultaneously in a single damage-dealing event. The Shaman's redirection effects modify that event to deal 4 damage to the creature with enrage and 0 to the Shaman, but the result is still just one event, which only triggers the Enrage ability once.