7.1 surround sound doesn't work

I bought the new Apple TV 4 mainly because it's supposed to support 7.1 surround sound but so far none of the apple-purchased films that indicate they have 7.1 surround sound will play with anything other than 5.1. My OS is updated to 9.1 and my connections are all HDMI.

Nearly every forum I've found on the topic of trouble shooting 7.1 surround sound issues with the new Apple TV focuses on content that the user has ripped themselves but my issue is that I can't get iTunes-purchased movies (The Martian, Terminator G, etc.) to play with full 7.1 surround sound. Connections are solid via HDMI, and blu ray movies play in full 7.1 but when playing a movie I purchased from iTunes via my apple tv, the highest sound quality I can get is 5.1. Why?!

I've checked and even swapped out HDMI cables as well as various HDMI ports on my Sony AVR to ensure that it wasn't a problem there. When setting the Apple TV to Audio>Auto, I get LPCM and when the Apple TV is set to Audio>Dolby Surround, I get 5.1 (Not 7.1)

Is anyone else seeing this issue and if so, has anyone else gotten the content to work?