Hypersmurf
Moderatarrrrh...
As for heighten magic metamagic feat, could you not use it to alter an already affected by metamagic feats spell so that it actually casts a double empowered fireball as a 7th level spell? Seeing as you set the level of the spell and if you don't believe that heighten spell adds +1 to the spell level everytime, one could just alter it in this way, unless this has been answered in some FAQ and I missed it.
From memory, they FAQ'd it to say "Apply Heighten before any other Metamagic Feat".
But a Double-Empowered Fireball is a 3rd level spell that takes up a slot 4 levels higher. A Double-Empowered Fireball Heightened to 7th level is a 7th level spell that takes up a slot 4 levels higher - ie, an 11th level slot.
-Hyp.