As far as I understand, Strongarm Bracers stacks when multiple people pull enemies (it stacks additively in that if 2 people each add 30%, you get 60% damage instead of 1.3*1.3 = 69% damage). In Patch 2.3, Threatening Shout: Falter has been redesigned so to "Enemies take 25% increased damage from all sources for 6 seconds".
Does this stack with multiple party members, like Strongarm does? Does it stack additively in the same pool as Strongarm and other 'enemies take more damage' effects?