Its really weird interaction. Technically, damage from twisters spawned by etched soul is not damage of channeling skill, so it should proc six-piece bonus. But its not. Twisters proc it only when it used directly. It is supposed to work like that? Because than i think description is needs additional information.
Neither the spells cast by the old etched SIGIL proc the 6-piece nor the new etched SIGILs twisters proc the 6-piece bonus. Seems like a case of procs don’t proc procs 