on your computer either wirelessly or by Ethernet. You can connect to the amp by analog, using the DAC in the Node, or digitally, using the DAC in the Onkyo. You then can compare Airplay vs WiFi/Ethernet and decide what you prefer.
I haven’t listened to Airplay critically, so I can’t tell you how it compares to the other modes, but my bias would be that it wouldn’t be as good as Ethernet or WiFi