Hi there, just to clarify, are you referring to his Rage effects or his Overpower buff? His Rages are passive effects and shouldn't be prevented by Soul Imprisonment, since that only reduces the chance for Buffs to activate by 100%. The Overpower buff he gains is an active buff though, and should be stopped by Soul Imprisonment.
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Thanks @Afrid. Yes, I was referring to the rage node. Sorry for not making it clear.