Hey, so basically it was just tradition. they don't need it slotted into their bodies, I just figured that'd be super cool, and that it'd tie in with a thing I had in-mind. Also with the sound part, basically when light and sound are trapped in the same container the hertz of the sound increases by some crazy amount by like a hundred million hertz or something along those lines. 

But yeah basically having them just use the stuff externally would be for the best. It'll give them a bit of a glass cannon vibe.