The Agent names seem a bit more empirish. Personally I like Imbue Agent first, then Empower.  Having the same prefix 'Imbue' common in both kingdom and empire makes a certain amount of sense.

I guess I was thinking that both Empire and Kingdoms would have 'Champions' and that the imbuing of them would be the same on either side.  It is the same use of magic and doesn't require any balancing if it functions similarly for both sides.

Adjunct would be another term that would work, Imbue Adjunct..