Tibo, I am setting up electronics for my incoming armor (ready to wear, because I am not good in manual works).
However, with my few knowledge of electronics, I guess I will opt for the iComm + Aker to have more quality, volume and static noise (to be put under the chestplate), a mic attached with velcro inside the helmet with the cable connected to a "input-input" adaptor for mini-jack (attached with velcro inside the helmet): in this way I will have the jack cable from iComm to be attached to the second input of the adaptor inside the helmet.
Another solution that I am evaluating (but I am not sure about it because of battery consumption, among the others) is to place a bluetooth receive in the helmet connected to the mic, and a bluetooth receiver under the chest, connected to iComm. However, I don't know if the receiver-transmitter can transmit the mic signal without a mic amplifier in the middle.
That's my idea.