MK5 USA platform uses a slightly different board setup to every other MK5 region and can't run anything else. Aussie MK5s will run everything except USA software (for the same reason), but may require different things depending on the region e.g. if you run NZ chips in a NSW machine (why would anyone bother!*) it will crash while loading as NZ games don't like the LAB board being installed.
Running USA software (even the setchips) in an Aussie MK5 will give a video crystal error, and running Aussie software in a USA MK5 will give a DRAM Emulator error instead; both won't go any further than the POST so you won't even see the game start up. Non-USA casino software (e.g. ex Star or Crown or Dunedin or whichever other casino they came from) will run on a standard Aussie MK5 but you will need the appropriate base chips to go with the games (this is the only time base chips are used on a MK5, unlike with MK6 where absolutely everything needs them), and will most likely need some way of bypassing the ASP protocol in order for them to do something useful (as with QCOM, the games phone home every second or so and will disable themselves if they get no response). Some regions may also require 3 batteries instead of the single battery found on NSW boards.
MK6 boards (both original and XP types) are universal AFAIK, but to convert a USA machine to NSW you will need the LAB board and anything else that is missing just like with the MK5s.
* NZ games have a paltry win limit of $500, thus the games tend to have crippled paytables and/or tiny max bets like 45 or 100, making sure the max win is nowhere near $500. Not only that, the $500 cap also applies to the entire paid game, including free games, so if you get to $500 inside the feature it ends abruptly at that amount and voids any leftover free games. Unlike USA however, NZ seemingly has no credit limit and will happily keep well over $2000 in credits (it's probably limited to 1000000 credits like NSW though, haven't tried).