Hello.

I can recommend looking into https://www.nordicsemi.com/eng/Products/Bluetooth-low-energy/nRFready-Smart-Remote-3-for-nRF52-Series

Unfortunately it is not based on the Zephyr, however it implements audio streaming using Opus and contains an optimized version of the codec

(with reduced memory requirements as well as using DPS extensions available on the Nordic chips).

If you require any further information, feel free to contact me.