I'm getting tired of trial and error
I share your pain, I'm struggling to get to grips with the user/group handling on the DNS-323 (which is more about my lack of understanding of how those things work on Linux than anything else) and how I map that in such a way that I can provide private areas on the NAS for each member of my family, inaccessible to the others, whilst providing a shared area that everyone can read and write. In a business environment it must be a lot worse.
However, to answer the question in the thread title, I'd say that as far as Windows ACLs and the DNS-323 are concerned, never the twain shall meet. The NAS neither knows nor cares about Windows users, AD or otherwise, and short of rewriting the firmware I cannot think of any way to get it to do so. The best you are going to be able to do is set up one DNS-323 user per Windows user but even then I'm unconvinced that I can get things to work as I desire them to without resorting to manual changes to the file permissions via funplug (YMMV obviously)