Fenix is equipped with an extremely complex sound package. Because of this, it is important that you set all (except music) sound sliders in the MSFS to 100 (MAX) in order to get the most out of it. It is also recommended to set "HEADPHONE SIMULATION" to off, "ACTIVE SPATIAL SOUND" to off and Window's own spatial sound to off too.
As of 7/11/22 - v1.0.6.146, we have now tied the environment sound slider to the cockpit wind noise. We recommend leaving it at 100% which will give the most accurate experience to the real A320.