80% from BoM, 50% from Together as one (rune on Call of the Ancients) and 50% from striding giant rune on Wrath of the Berserker granted through wearing Morticks brace is the baseline.
DR=1-(1-.8)(1-.5)(1-.5) = 1-(.2*.5*.5) = 1-(.05) =. 95 =95% DR
I can’t speak to working in 2H90 as I haven’t tried it, but interesting idea.