Hmm, I can only answer partially... Only have played GS build and 3XFlash Freeze, what I do, is rotate my major essence based upon Tyrannical. If Tyrannical I use Condensed Life Force, if not and we need more AoE damage then I'll go "beam on death" Focusing Iris major.
Problem with maintaining multiple sets of gear is the secondaries needed are different, and you complicate it further with Fire gear set.
Why don't you just run Fire in M+?