SocioPhobia
If I am right then In sound magic he vibrates the molucules. Shouldn't the fire have a deviant that could control kinetic energy as air is controlling vibrations. Well if he could control kinetic energy then he doesn't really need to have an ice deviant. He could freeze ( stop the movement of molecules) the things around him.
Make him train his primary elements first the fire and wind manipulation more and make techniques for fire like endeavor's he'll spider or an sword slash made of intense and concentrated heat or laser beam or cero like plasma cannon and for wind air bullet or air cannon or windo slash. Or maybe train more his energy or mana manipulation like making mana construct or maybe train him to do rasengan, it's just an advance energy manipulation..... .................................................................. Just my opinion to, you know make him a bit stronger with many technique in have arsenal.