I am planning on buying a 7.1 audio setup in my new apartment with a Dolby Atmos compatible receiver (DENON AVR-X2800H DAB). I will mainly use this setup to watch movies and shows on my Apple TV 4K via the Apple TV app. Most movies and shows on Apple TV have 2 available mixes: Dolby Atmos and 5.1.

What would happen if i played a Dolby Atmos & 5.1 compatible movie on my 7.1 setup? Will the Dolby Atmos mix adapt to my non-Atmos setup and output a 7.1 mix, or would it go for the 5.1 mix and leave my rear speakers silent? I am trying to figure out if getting a 7.1 setup for my Apple TV is worth it or not.

Thanks in advance for the help!