[noggin]

So ATV4K: no atmos, no passthrough, no 4K YouTube

The Apple TV 4K does lossy Atmos audio when using copy protected video streaming Apps like iTunes, Netlix and VUDU.

It cannot do Bluray Rips Atmos Audio passthrough.

Also to add is the Shield does below average 1080p > 4K picture upscaling. Kodi Leia has a workaround for that within 1080p / 4K resolution switching, but other Apps miss out.
The Shield also has no Dolby audio license to support older DD only equipment and no DolbyVision support if you have a 4K DV TV and Apps that support that type of HDR.

There are other limitations .....

Read the linked sticky threads at the top of the forum, there is already plenty of information already written about various platforms limitation and ongoing problems.   

Sorry for the necro bump. But: waaaaaaat? The NVidia Shield won't pass true, or decode into multi-channel LPCM, good old Dolby Digital? That means that you cannot listen to 5.1 sound from DVD images? Is that what not having the Dolby audio licence means?  

No...

The Shield TV issue is that if you watch Netflix or Amazon Prime DD+ content via their Apps, the Shield can't transcode this to legacy DD within its Android TV OS, nor can it decode to PCM 5.1/7.1 within its OS.  It can only bitstream it (or decode to PCM 2.0?)

Within Kodi you get full DTS HD, Dolby True HD, DD+, DD, DTS bitstreaming (and I think True HD + Atmos and DTS:x) plus you get all the Kodi options of PCM 5.1/7.1 decode and transcode to DD - as Kodi handles that, not the Android TV OS.

The limitation wrxtasy is talking about is purely a limitation when using the Shield TV with the Netflix/Amazon apps with a non-DD+ compatible amp, because nVidia can't do a DD+ decode in their OS build as they don't have a DD+ licence.