Airplay on MAC:
Go to settings in OSX - sound - Output: Airplay
Airplay on PC:
To use airplay on PC you have to install Airfoil: https://www.rogueamoeba.com/airfoil/
You must have the latest version to make it work. To be able to stream HiFi you must use the Web Player.
(HiFi mode will not work through the desktop app, only High & Normal mode)