The TV part of the Apple TV name properly evokes that it’s built as a device to play video. It also has a screen-based interface for navigation. The new Apple TV goes a step further by adding support for richly rendered, smooth-motion games, and opening it up with an App Store. But the Apple TV, past and future, is full of music and spoken words, too—many people also stream audio from OS X and iOS using the Apple TV as an AirPlay target.
Which is why some owners of current models and potential new buyers were dismayed that Apple dropped the optical-audio port in the content box’s new design. That port could output plain old analog stereo signals, as well as encode richer digital audio—including 5.1 and 7.1 surround sound—using the Toslink optical interface. (AirPlay and older Apple TV models support 5.1 surround sound, while the new Apple TV can output both 5.1 and 7.1 but only via HDMI. It’s unclear whether an AirPlay revision will add 7.1 with the new Apple TV.)
Read more here:: Apple TV drops optical audio-out: How to pump up the volume again