Hee hee had to deal with this questoin with a Rogue of mine. From the official WoTC OA FAQ;
"If you use a dastana or chahar-aina that has an
enhancement bonus, does that bonus stack with or
replace any enhancement bonuses the foundation armor
might have? If you’re also using a magic shield, how does
using a dastana or chahar-aina affect that? What
happens if the armor and the dastana or chahar-aina
both have additional special properties?
When you add a dastana or chahar-aina, you get either the
enhancement bonus of the added piece or the enhancement
bonus of the foundation armor (not a shield), whichever is
bigger; if you add both a dastana or chahar-aina, you use the
biggest enhancement bonus of the three.
A magic shield’s enhancement bonus still stacks with
whatever enhancement bonus you’re using for the armor
you’re wearing on your body.
No matter which enhancement bonus you use for the armor
you’re wearing on your body, you get the benefit of any
special armor qualities any of the items you’re using have,
except that similar qualities don’t stack. For example, you
wear a +3 chain shirt of light fortification, a +2 dastana of
spell resistance (13), a +1 chahar-aina of spell resistance
(17), and a +1 shield of heavy fortification. Your panoply of
armor has a total enhancement bonus of +4 (+3 from the
chain shirt and +1 from the shield), and you benefit from the
heavy fortification and spell resistance (17) qualities of the
shield and the chahar-aina."
So no, the armor bonuses do not stack. I ended up keeping them though just to stack abilities more than anything but only left them at the required +1 armor bonus since it didn't mean anything. That still doesn't mean you just can't take the Armor Focus Feat from the OA book for each piece and still get a +2 to the AC for each piece I was wearing
