HTC recently updated its Connect app with a nondescript change log of "Increase new wireless protocols." It turns out, that new wireless protocol is Apple's AirPlay platform. Meaning, owners of the HTC One M7, One M8, One M9 and the newly released HTC 10 can now stream audio to an AirPlay speaker or Apple TV from his or her phone.
To use the newfound feature, you'll first need to install the updated HTC Connect app from the Play Store. With it updated, you can connect to an AirPlay device two different ways.
You can swipe up on the screen of your phone with three fingers to bring up the HTC Connect dialogue. Your phone will automatically attempt to reconnect to the last device you used, or you can pick another device by tapping on Choose Other.
Alternatively, you can open Settings > HTC Connect. Here you'll find a list of available streaming devices and the respective protocol each one uses (Bluetooth, DLNA, AirPlay, etc.). You can limit the type of devices that show up in this list by tapping on the menu button, followed by Scan Option.
To stop streaming from your phone to another device, pull down the notification shade and close the notification indicating where the audio is being sent.