This is fine, if your NAS box as hdmi port, you'd have no issues using a receiver with it.
However, I'd recommend against it. Your best bet would keep your NAS out of sight (and ears) and use small and inexpensive (and much more versatile) media client like Roku, FireTV, Chromecast or my fav (and most powerful by much) suggestion - Nvidia ShieldTV. Since the later is likely more powerful than most NAS boxes processors, I'd use it to run both Plex Server and Client and use nas for storage and other things.