If NZ is like the UK (which is likely as it's a former colony, and still has close ties, and very similar laws) then there is no import duty on personal posessions, regardless of value. You may have to sign something saying you will not sell your gear for 2 years.
External step down transformers are inexpensive, and according to a couple of manufacturers I spoke with, work just fine, causing no audible degradation, provided you get a suitable power rating.
If you end up deciding to stay in NZ permanently you can always have equipment modified later.
It's a beautiful place. If it were not for family ties to England and the US I'd move there in a hearbeat.