These headphones work wirelessly via a Bluetooth connection. To use them wirelessly, activate pairing mode by holding down the power button for 2-5 seconds until the blue light flashes, then connect them to your Bluetooth device, such as a smartphone or computer.

For use with an Onkyo amp, if it doesn't have built-in Bluetooth, you'll need an external Bluetooth transmitter plugged into the amp's audio output to transmit sound to the headphones wirelessly. AirPods also require a Bluetooth source, so without a Bluetooth transmitter on the amp they can't be used directly wirelessly.

In short, these headphones connect via Bluetooth, and for a non-Bluetooth amp like a classic Onkyo, you need a Bluetooth adapter to use them wirelessly.