To answer your specific question:
Yes you are permitted to fly AKL-MEL-SYD-EZE...
The Circle Pacific fare is really quite restrictive
The One World Explorer ticket is much more flexible and if you are flying economy then the ex-Auckland 4 or even 5 continent explorer ticket is cheaper than the 29,000mile Circle Pacific ticket (and the 6 continent ticket is only NZD200 more)
This 5-continent itinerary will give you the stops you want
I suggest you read the fare rules on the One World web site and play around with itineraries to work up one that suits you