the way i see it though, unless you are making a barb or a pally using enigma a low str req norm armor is not that much different, yea u are losing around 400 def but any char besides a barb or pally has crap for def anyways. basically take your biggest str requiring item, subtract roughly 70 str (approx str from enigma) and that str number will be what u want to spend str on.
a nec wearing a breast plate enigma will get hit the same amount as one wearing an archon enigma. for low def chars its all about blocking and damage mitigation i.e. DR, damage absorb (Energy shield, bone armor ), damage taken goes to mana.