Has this ever been tried before?
Throat mics for PMR/Cobra radios are becoming cheaper by the day.
Would it not be relatively easy to rig up a throat mic, hooked to a radio mounted either in the helm's rear, or in the armour somewhere... And have ANOTHER radio tuned to recieve stashed somewhere else about your person? I can't see there being any danger of feedback / howlround with such a setup... The only problem might be if your channels clashed with someone else!
Or is this a mince idea? :p
If so, surely the throat mics could be adapted to wirk with a simple speaker / amp rig too?