Can we ship our 2 TV's and stereo system to NZ knowing they will work fine or will there be problems with voltage/connectors/ cables and all those sorts of things?
TVs should work as long as on the back of the TV it shows input voltage around 100 - 240 VAC (typically switch mode power supply). The TV tuner won't work in NZ so you'll need to use them in 'monitor' display mode and connect to an external set top box.
and a Sony stereo receiver with Kardon speakers..
I've found stereos to be less accommodating to multi-voltage. Look on the back to see input voltage rating (ie. 100 - 240 vac)
IMO, best to buy in NZ