If one video stream is HDR10 and the other Dolby Vision yes it is a dual layer Dolby Vision video.
AFAIK there is no way currently do play dual layer dolby vision / True HD Atmos (the flavor you have on UHD Blu-Ray discs) on Apple TV.
And it is not easy because Apple does not support or allow it. The Firecore Infuse team is certanly trying hard to do it.
I use a clone of Oppo 203 with a special firmware to play Dolby Vision+Atmos from my NAS. It works great (although MKVs from animated movies have audio-dropouts in their Atmos tracks) but is nowhere as convenient as Infuse.
So the only hope is that the people at Infuse will find a software solution to manage the “double layer” with the Apple TV 4K ? Is that technically possible ?
No it’s not possible. You will need a program like dvdfab to remux/reencode all of your files to single layer. This is a hardware limitation by Apple. I doubt Apple will ever support dual layer as that’s a format found only on discs. All streams (and the content Apple sells) is single layer.
But why can’t I play « single layer » Dolby Vision / Dolby Atmos files that are in my NAS with Infuse and my Apple TV 4K ? As it is said that Infuse can play « single layer » now ?
Since you can only make an mp4 with Dolby Vision to play in infuse, you can’t attach atmos to it. You can check the makemkv forums for ways to attach other types of HD audio to single layer DV mp4s that you rip. I think people have had success with e-ac3, but it seems kind of complicated. Some people aren’t quite happy with dvdfab’s DV mp4s either.