We're on Inferno and getting absolutely torn up by his spread chain attack. (We've tried it as solo Wizard, solo Demon Hunter, and as a pair together.) There seems to be little pattern to when he uses it, and its random damage has hit for upwards of 40k at times, enough to one-shot. Even with 2400 armor and some extra physical resistance, I'm taking enough to survive with less than 3000. Is the only solution to stack more armor and vitality, or are we missing a tell?
I've only seen the spread chain attack at mid-far range. Up close and personal may seem dangerous, but it's probably your best bet. Tip: Make sure you avoid his large swing and knock back at a reasonable distance. Rather than using chain, he will typically charge, allowing for easy damage when stunned.