[Alneyan]

Empowerment proper does work, as it raises the basic level, but I believe it is what you meant. Everything else will be void.

I believe the Banner of the Northern Star might work too, as one of my mages survived a lot of Magic Duels with this item in hand, and +6 in base astral; he could have been very lucky though. On the other hand, a +5 mage with the Banner and Power of the Spheres will get killed very quickly.