Todd,
I think you'll find most of us don't use any means of amplifying the sound into our helmets. I can't always hear very well inside my helmet but I hear well enough to not run into something or crush small children (much/often). If I'm about to get into trouble usually there is a handler, or an annoyingly agile biker scout, nearby to assist. I think more folks have an external amp that projects their own voice.
I suggest getting out and trooping before you decide to modify your helmet in ways you may regret down the road.
-Eric