Wow, thanks for all the detailed and researched replies, xiaofan. Definitely some useful information there and I appreciate the time and effort you have taken.
Some clarifications I need to make :
1. I have Bluray remux files on my old PC, both 4K and 1080p ones. I wish to be able to watch these on my TV, either by streaming them through the network(Ethernet), or having a physical device plugged to the TV (whether it be a HDD or media box).
Firstly, will a plugged in HDD be able to pass through the high-def video and audio embedded in these files to the TV and soundbar, so that I can get full 7.1 or Atmos sound,etc? If so, it would be the cheapest option but troublesome if I have to keep unplugging it, transferring files to it and then plugging it back in.
Secondly, will Plex work in this case? Have a Plex media server on my PC, use the Plex app on my TV to use it to direct play? That means, the TV and soundbar handle the decoding etc.
2. I also wish to be able to play the physical Bluray UHD discs. Do I have a better choice other than getting a Bluray player? (besides the Xbox One X/S) Meaning something that would be able to also help in number 1 above. I realise the Xbox One can do that, but I'd rather not have to use the interface. Would the HTPC be better in this regard, since if I have a Bluray drive it can play the discs, and also do everything else that I want?
3. One more thing I didn't mention earlier is that I wish to be able to play apps like HBO Go, Singtel Cast, Starhub Go etc as well. I'm under the impression not all boxes can handle this well. I haven't really decided on whether to subscribe to a full fledged cable tv package, and as such these apps would be more important if I don't actually do it. Between Nvidia Shield, Apple TV 4K, Amazon Fire Stick, Roku Ultra, which one would you recommend?
Also, are these Android media boxes, Apple TV etc of importance to me only if I want the apps on them, or do they offer me more functionality that I need in these situations? Since they offer a way to stream the files on my PC to my TV, through Kodi or Plex, then they seem to be a viable option. But I'm just wondering if they would be able to serve all the above needs or I would be better off with HTPC.
P.S. One thing I'm confused about. Even if I use these media boxes, and they don't have support for certain things like Dolby Vision etc, if I'm just streaming files from my PC, the TV and soundbar are the ones handling them right? The boxes are just passing through the information.