ok, so if somebody steals say, my commander (its a creature) with an {Argentum Armor}. When it attacks, who chooses the permanent to blow up?
I believe you do. You still control {Argentum Armour} (assuming you cast it ect). It doesn't say "equipped creature has blah blah" it says "whenever equipped creature attacks blah blah". If it said "equipped creature has" then it'd be considered to be printed on the creature.