Is it possible for a monster to stack these feats on the same ability? For example, could a pit fiend, caster level 18 take empower SLA and apply it to fireball in addition to the quicken SLA he already has applied to it?
By the rule for Quicken SLA, the creature can only select a spell with a spell level equal to half of its caster level -4 this would still seem to be possible. An empowered fireball is a fifth level spell. And half of 18 minus 4 is 5.
Does this seem doable or is there a problem with my math?
I always believed you could and should combine. But they are expensive feats for the effect...