W.r.t. optimizing Deafening spell, a good delivery mechanism is via deafening spell sculpt spell hail of stones a no save / no SR effect.

W.r.t. increasing the power of deafening, it seems that optimizing for the removal of other senses will increase it's effectiveness. Hence, an invisible spellcaster with invisible spell summons can spike the battlefield via Deafening spell. Even against a foe with true seeing, you could still optimize Hide and then use Deafening spell + Darkstalker to be undetectable---and that's true even if you are casting spells with verbal components.