I'm also using the Aker voice amp behind my chest plate. It works well, but care has to be taken with volume settings and positioning the mic in the helmet to avoid feedback. The wires are a little bit of a hassle, as they have to go underneath the underarmor, then come back up behind the armor to the back of the chest plate. One big plus with the Aker is that it holds a charge for a long time and the batteries are rechargeable, so you just have to plug it in recharge it before each troop without having to worry about changing out batteries.
What I'm curious about is whether anyone has taken an Aker apart and been able to place the electronics in the helmet with mike tip speakers.