I was actually pretty delighted over the ilvl516 caster staff and caster head when i got them the past days - at first ... but only until i found out that i could neither use Eye of the black Prince on the Staff, nor put a Meta Gem into the Head - the heroic one in my case.
That not only degrades the loot, esp. the Head piece, but only makes me wonder, why on earth i actually did the heroic quest chain at all ...
Maybe you want to change that and make both 'enchants' applicable on these items as well?