Connecting Onkyo TX-NR515 to AirportExpress

0.- Connect the AirPort Express to the ONKYO A/V via an RC cable.

1.- Set the AirPort Express with AirPort app (in Utilities). I set it up as joining to an existing wifi network.

2.- Once finished, you have the option to choose which sound output you want. For example, if in iTunes you can select which speakers to choose in the airdrop icon. If you have, e.g. Spotify, select the airport device on the sound icon which, of course, is a valid option to output your system sound as well.