If you wanted Auto Import to run automatically with your new NAS, you may be able to find a setting on it to tell it to generate "File System Events" properly. But as Brian says, some NAS do not report "File System Events" properly.
The reason Auto Import does not run automatically when it should is that a NAS may be telling MC it will send "File System Events", and then it never does. In that case, MC never runs Auto Import, because it is waiting for events to be reported.
If a NAS says it won't send "File System Events" then MC just runs Auto Import on a regular timed basis, so it still works. So actually turning off "File System Events" reporting on the NAS may make Auto Import work correctly, with a slight delay.
But the Toolbar button works fine as well. I often use it even though I have Auto Import set up to run in the background, because I want to see the files I just added imported now, and what the result is, in the MC Action Window.