Does Threatening Shout: Falter stack? [duplicate]

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?

No, it doesn't. Shouts of the same rune do not stack. Still, shouts with different runes do stack.