To convert a non JAR licence to a JAR one is very expensive. If you don't have 500 hours in multi crew aircraft it will cost at least $A50,000 and you must do all the JAR ATPL exams.
In NZ you to get the ATPL you must be flying multi pilot a/c. In Australia you don't. BTW there is no such thing as a "frozen" ATPL in NZ or Aus. You have a CPL with an IR and you have the ATPL credits. No one will know what you are talking about if you say "frozen ATPL". Also, something to note, you can't log P1/US time from the RHS in either NZ or Australia even if it is "your leg". So you need to get the command time prior to getting a multi crew job.
Getting work in NZ is quite difficult. Like Australia there are many qualified pilots out there and too few jobs.
Many Kiwi's go to Australia to look for work. The NZ and Aus licences are interchangeable.