In the API Examples for the Callback file there is no instance of Balance2 in the example, but there is a separate Callback option in Poker Mavens for Balance2 in the Callback system.
Is it setup identical to Balance and would look like below or are some field names different?
I haven't updated that page since the secondary currency option was added in Gold v6 but if you click any event in System tab, it lists all the fields in the help bubble at the bottom.