Hello Akshay, I am using Nvidia Shield personally and I actually bought it few years back while travelling to US. To answer your queries ---
1. Nvidia Shield Pro will be fully functional in India with all the HDR and HDR vision or Dolby features except Nvidia Games.
2. It's just like an android media player so you can go ahead and purchase from Amazon or get it delivered from US. Doesn't matter
3. You can use the same power adapter and not required to use a step converter or anything.
4. Now if you are comparing it with Apple TV...I would say definitely go ahead with Apple TV and I am not sure where you heard about the atmos conversion to lossy digital plus but that is not true and Apple TV's PQ is absolutely stunning.
5. Also to be noted if you are using Apple TV and want to make use of HDR dolby vision or Atmos, you have to use the right HDMI cable. For example Belkin's HDMI 2.1 cable is the authorized one from Apple and I use the same.
6. In Nvidia you will have the option to use KODI which can be your personal media player for playing music and movies from your personal collection like USB, Hard disk or NAS. In Apple the features are limited to add a 3rd party media player like KODI except using few apps like Plex (not that great) or Infuse (not that great like Kodi and comes as a paid version)
7. If you plan to buy Apple TV, just wait for few days as they might launch a new version today.
Hope this helps...
