I don't use a DK Magika Tank but I would 5H 1M and 1L or 6H and 1L. I do have a magic Templar tank and that is what I use on it.
Sets are ebon and Plague doctor at the moment but probably going to try different sets them PD. As farm as helms I use Lord Warden now but may change to bloodspawn or 2 magic regen helms.