How to Control receiver with apple tv remote

By default, Onkyo receivers (at least the TX-SR606) On/Off can not be controlled via AppleTV/HDMI.

The reason for that is that Onkyo uses RIHD (which stands for Remote Interactive over HDMI) to control Onkyo connected devices.

In order to allow control by non Onkyo devices, you need to disable RIHD to enable CEC (Consumer Electronics Control) which is a standard supported by most providers.

On TX-SR606, this is done by entering the Advanced-Setup/Hardware-Setup/Control and selecting Disable (to disable RIHD).

for more details check the Onkyo receiver manual