That really isn't the point. A NAS is going to be a way lower power @ idle and under load. Plus what are you supposed to power your rig on / off anytime any family member wants to watch some TV?So much effort when a Chromecast ultra runs Plex perfectly fine.
-Need a computer that supports HEVC
-video card that supports your needs and Plex
-Decently fast spin point drive
-Chromecast plugged into your reciever (wired is better)
I just run Plex off my main rig and shut it all down when I'm done. Easy peasy. NAS is a complete waste of money / overkill. IMO.
A Chromecast can DirectPlay. But if you are streaming to family members over the internet then you may need to transcode unless you have a fancy internet connection.