This came up in our Second Darkness campaign today... yesterday. My Wizard is a Universalist, and he carries the Staff of Dark Flame found early in the AP. At level 12 I have 3 slots of Metamagic Mastery and wanted to use 2 of them to Empower a Fireball cast via the Staff. Legal? Not Legal?
The DM made a quick call and allowed it to work, but I wanted to run it by everyone here and see what the consensus is.
Since the spell is cast at your caster level instead of the staffs and because the metamagic slots are consumed, I can see some logic to allowing it to work.
But at the same time, since the spell is not powered by your personal spell slots, I can see logic to not allowing it as well.