I remember seeing a short picture tutorial of how to do it. But I have a pretty clear understanding.
Basically, you figure what points/corners of the armor (chest armor im talking about now) that you want the snaps to be on, you attach the female end on those points on the vest itself.
On the armor pieces, what I remember, is you take small squares of plastic, and attach the male ends to that, and then take the whole square w/ male end, and epoxy/JB weld/watever adhesieve you prefer to the actual armor piece, so that it is corrosponding to the female end on the vest.
Thats how I remember it, but it will make more sense in picture form.
I can attest to using snaps over velcro, because the velcro will have a tendancy to detach itself if you bend/move. Also, I had velcro on a custom made vest, and I had accidentally left it in a warm area, not even, and the adhesive that was on it, had melted or whatever and left a horrible mess, and complelty de-formed the vest itself. I have pics of it actually.. But thats my opinion!