All of the new streaming devices nowadays are all targeted at the "Gen Y" consumer who just wants to plop a panel on the wall and a streaming device so that he can do "Hulu" or whatever and he's good to go. These are no longer designed with the audiophile in mind. All the devices are like this (AppleTV, Roku, Fire TV). The USB-c port will not do a digital audio output. For Apple, it's meant for diagnosis and service/support only, which makes it completely useless to you.
---
Your only option is to get a new receiver that supports HDMI, because that is the only way you will be able to get audio out of the AppleTV device.
---
Your only option is to get a new receiver that supports HDMI, because that is the only way you will be able to get audio out of the AppleTV device.