Roon Core is intended for a PC-level CPU. These powerful NAS have PC inside.
Powerful NAS will have a fan and be loud with disks running, so it's not good for connecting the DAC directly, even though they say it will work. Maybe with very long USB cable? That's where microRendu or Aries comes in, to be a silent Roon player for the audio room with fancy iPad GUI, etc. But it doesn't have to do the database crunching like the Core part.