Official SE:IV Gold Patch 2 thread...

[Fyron]

Well... it doesn't stack literally. Take a 200 point shot, and EA with 50 HP and 20 Emmissive Ability. It hits the first EA, getting lowered by 20 points. Then, it does 50 dmg to the EA comp, lowering the remaining dmg to 130. It hits the next EA, getting lowered by 20 more points. The 110 remaining dmg applies to the EA, destroying it. The 60 remaining damage hits the next EA, getting lowered by 20 more points. The 40 dmg is then applied to the EA, but is unable to destroy it. So, the EA ability meant that only 2 EAs were destroyed and one almost destroyed, instead of 4 armors being destroyed. So technically, they stack, but not all directly into one super-emmissive pool. It is un-like Crystalline Armor in this respect.