It sounds like you have become "stuck", you have been asking these same questions in several threads over several weeks.
At some point I think this happens to us all!
The only way to decide what is best is to listen for yourself and make your own judements, you wont always find the answers you need on forums.
If you can not demo then you will be relying on others opinions...
IMO you have an excellent amp and headphones - you need to do them justice.
If you are limited to AU$300 and dont want to buy anything modded, then the NAD will perform the best. That price is really good, its a nice warm sounding player. No standard DACs < $300 I have heard will better it. I would say the modded Lite DAC Ah (approx AU$350 comes close, and probably equals the NAD). I have heard a stock zhaolu (AU$300) a couple of times and it performs about the same - does some things better (detail), some things worse (bass).
A modded zhaolu (OMZ) takes everything to another level but is going to cost more - worth every cent! This is where I ended up after listening to various DACs / CD players in your price range.
Dont be scared of buying a modded DAC - many come with excellent service and support (COEM, Ori etc.)
Good luck with your decision.