He wasn't using Djem So at that moment though. Djem So uses a different set of principles, from what we saw in that trailer.
No he wasnt using djem so allthough it will be impossible to tell obviously, but its irrelevant im not even trying to prove that malgus uses djem so in that trailer. why do you think i was? read the posts again
But it proves the point doesnt it?! Powerfull atacks can be made using duel wield.