I have to add... Your foam build is looking great. (yes I just HAD to have a look)
As a side note: I have been a subscriber of both you and Cereals builds since the beginning of both threads. Gotta keep learning (lurking) new things.
The voice amplifier is really just a pair of computer multimedia speakers that I removed from their housing and installed it into the back of the torso. They are powered by a rechargeable Lithium Ion battery pack. The Mic is connected to the smart phone, the smartphone is also connected to the line in on the speakers. Its all wired. (Sorry I do not have a circuit diagram.) The smart phone runs an app called "Megaphone". That's how my voice amp works. This configuration also enables me to play music and answer the phone. The mic is part of half face mask that I wear under the helm. That way I can remove the helm and still have the voice amp active. The helm fans don't really interfere with the voice amp that much, it does pick up the noise a little, but in the convention environment, it is not noticeable at all.
The smartphone ALSO controls the GoPro via WIFI. With that, I can control all the settings, turn it off, turn it on and even preview what it is seeing and hearing.
I also carry a Blackberry Playbook in the back pouch, that can do the same thing. It offers a bigger screen and can be handled by my handler/photographer or to show others just how interactive the armor really is. (video on this in the near future)
As for the GoPro mic and fan issue: I just picked up the external mic adapter. With that, I will be able to use an external mic that I can place on the outside of the helm, away from the fans. A test to see how it sounds and works, is planned in the near future.