Don't know if it makes sense almost one year after opening the post but:
There are a few differences in HW between OXO and OXE.
First of all teh OXOs have several rack-types "normal rack" and "mega-rack". - The OXE official only runs with type "mega" but i tried in lab and it still works with both of them except of some boards in slot 5-8.
Another difference is the USB-Port in front of the CS / CPU. But it only spends power, right?!
And of cause the daughterboards for VoIP are different! Looks in deed similar but are not exchangable!
Anyway, you can change the software of the different HW if you want to.
I allready flashed an OXO to an OXE and it works soooo fine!
Regards
-Tobert