The observation that it just sounds like some American bloke and that the creature's gives hardly any indication that the sound is coming from it's head.

At least Ackbar is doing his Sir Robin Day impersonation which makes him sound a bit like some alien creature attempting to speak English (or whatever they are calling it in the Extended Universe). At least his face (especially his mouth) and body move like he is the source of his dialogue.

Making the line come over the radio connects that ship to the larger fleet (like the pilot chatter in the Yavin base during the first Death Star attack).

As the line currently plays out, it sounds like an unalien alien throwing his voice out of a mask-like head on a hardly manned bridge of an empty ship that has little connection with the larger fleet.