Thanks for your suggestions.

Seems like OW AirPass is better than *A one since OW pass only requires 2 segments.

But there is something that I am a little bit unclear about. Website says that OW AirPass can only be purchased on return fares. What if my flights are FRA-SYD-FRA and then another FRA-SYD-FRA? Does this qualify me for OW European AirPass? After all, my flights are return flights and I am travelling on a non-european passport.