A year ago, I visited a friend who introduced me to this whole concept of watching movies on a computer to a TV. Before, I would watch optical media (DVD, Blu-Ray). He had 4 ATVs in his house with a huge movie collection. He turned me on to this concept and before that, I never knew what the ATV was...I thought it was a TV😱. I turned him on to Macs because when I showed up with my MacBook Pro, he ditched all of his PC's and bought 5 iMacs and a MacBook Pro.Interesting thread!
OP - A couple of things I thought whilst reading it:
Are you tied to the Apple TV as the streaming player attached to your TV? You seem to want to (ideally) stream from the NAS without a computer switched on to run iTunes at the same time. As already mentioned by others, it's only possible to do this in a limited way with Apple TV. But with a Smart TV, Roku, Amazon Fire TV, Xbox, or Playstation as your streaming player you can just directly connect to a shared media folder on the NAS. You can alternatively install clients (such as Plex or DS Video) on some of these devices for media servers running on the Synology NAS.
You seem to have a bit of concern about wifi performance. At my home I had problems with streaming HD content over wifi to a weaker signal area of my home. I now use powerline networking to connect my router to my TVs and their attached devices. Powerline networking is cheap and I'm very happy with the result.
My setup is Airport Extreme connected via its four ethernet ports to cable modem, Synology NAS, Powerline adapter, and Sonos bridge. Next to my main living room TV is a powerline adapter connected to a network switch. This network switch branches out to the Smart TV, Apple TV, and XBox. In another room, I have another powerline adapter connected to a Smart TV. I usually access video content stored on the Synology NAS via the DS Video application on my Smart TVs.
Since then, I have 2 ATVs that I bought and am using for this. I do not have an account to Netflix and my Panasonic Plasma is a smart TV with internet connectivity but it is not connected to the network. I have a huge movie collection that is now on an external HDD connected to my PC. When it is movie time, I turn on the PC, open iTunes and make sure the external drive is on. This is the only way I know to do what I want to do and it works well for me. I am not set on anything at this point but I realized that my 2TB external HDD is filling up fast and I will need to get a bigger drive to store my media. My friend had the Buffalo linkstation NAS that he uses to store his media on and his iTunes library points to the NAS as the directory for media.
Since he switched over to all Macs, he bought a 2TB Airport Time Capsule and a 4 ro 8TB G-Tech G-raid usb3.0 which are attached together. He bought the time capsule because he needed a good wireless router and is using the time capsule for backup that everyone in his house backs up to. His G-Raid has all of his media on that his iMac accesses via iTunes to stream to the ATV. So I thought that would be a good setup for me so I can have the media on a location that my kids can access if they want to as well as me and also to make backing up easier for everybody.
I don't understand what these media servers are such as Plex, Kodi/xbmc but I don't want to obsess with all this stuff. If there is an easy way to do what I want to do and that involves using a media server such as plex than I would love to hear how others are doing it. I don't have a lot of $$ to spend on this stuff but I know I need to change my storage and backup to accommodate a growing collection. Since I have already invested in the ATVs, I would like them to be in the mix and part of the solution. I know there are many people that are ditching their ATVs for other devices because the ATVs and iTunes have many limitations compared to other devices and media servers. Speaking of which, one thing that I am frustrated with is ATV not supporting DTS audio, because my ATV is connected to my Yamaha receiver and I have a 5.1 setup with speakers and a sub woofer.