Ok, I'm not sure I'm understanding some of the arguments above, since they appear to be based on assumptions I'm not willing to make.
So here's my understanding: The rules state regarding enchanted items that "Defensive items (ones that provide armor or a block, for example) often consume a use at the time of defense and don’t require a separate action to activate" (YS280). I tend to read the implication here (which isn't stated outright) that all other uses on an enchanted item require an action to trigger the effect.
Because of this, it isn't possible to use two enchanted items as part of an Off-Hand Weapon Training combo, since each of them would require an action to trigger. So, for example, a character with Off-Hand Weapon Training and two enchanted swords (each with an inherent weapon:2 and some number of uses of a weapon:10 attack) could do any of the following:
1) Make a melee attack, which would be at at weapon:3 due to the stunt
2) Trigger his right-hand weapon's enchantment, which would burn a charge to create a weapon:10 effect aimed by Weapons. At most, this would count as a weapon:11 attack due to Off-Hand, though see below.
3) Trigger his left-hand weapon's enchantment, which would burn a charge to create a weapon:10 effect aimed by Weapons. At most, this would count as a weapon:11 attack due to Off-Hand, though see below.
He could not trigger both weapons together, with or without the stunt, because this would require two actions.
In fact, I personally would take this further by ruling that Off-Hand Weapon Training only applies to actual melee attacks, not to magical attacks that happen to use a weapon as their focus. Say, for example, a wizard had the Off-Hand stunt and carried a weapon in his left hand. Then he cast an attack spell, and described it as, say, a burning sword that appeared in his hand, then slashed through his foe. (Fire spell, 6 shifts, weapon:6 spell attack.) Would you let him add +1 to the strength of the spell? A spell effect generated by an enchanted weapon should be treated the same way.