For Expert product:
To stream music to a Devialet you will first need a dedicated network. Please find more information about how to set up an optimized network here
In such a configuration, you can connect your Devialet via Toslink to your Airport Express. Now you can use the Air-Play to stream music to your Devialet.
For Expert Pro with the Core Infinity:
Expert pro and its Core Infinity board are natively Airplay compatible.
Once you set up your system, you will be able to see your Expert Pro with Airplay to stream music on your amplifier