I have read many times on the forum that it only changes the third one. But it would be nice if it is all. Who really understands Cadence…
I think that the mechanics is such that DM is a global bonus and therefore it is converted only with global conversion but if Cadence has conversion then for the third hit that damage is converted because it is added as flat for that Cadence hit. Seen somebody somewhere say this (even many times).
I found the discussion about it here.