I have a Zidoo X6 and can confirm it works.
I also have Nvidia Shield TV and can confirm it works.
So I assume it works with HiMedia H8 since it's the same chip as HiMedia H8.
Even my 5 year old WD Box has TrueHD and Atmos works.
All you need
1) TrueHD 7.1 ch HDMI passthrough.
2) Atmos enabled receiver.
I also have both devices you mention and yes the Zidoo plays atmos but I get sync issues as someone on another thread said their himedia does. The reason for posting is you said the shield passes atmos to the amp, that's rubbish it doesn't theirs posts all over the Web about HD audio not working and Nvidia are hoping to fix this issue in a update at some point but I wouldn't hold your breath. I don't know what available amp your using but I can assure you atmos doesn't work I'm sure it defaults to multi channel, I have atmos speakers and a onkyo 636 amp and when atmos is their it says so in red.
I have a himedia h900 I bought from futeko and that plays atmos. I long for the day when we can buy a media player like the h900 or the WD live that don't require android and jumping through hoops to do what they were bought for. I just want to turn on my media player and play my files without using a buggy hacked version of kodi that always has some issue. Futeko why can't you get some proper media players like the old ones that do 1 thing play media nothing else, it comes to something when I'm using a 6 year old player because my zidoo and shield can't do the job.