How to generate sound in Unity and in plugin simultaneously on iOS

We are creating a plugin for voip integration in Unity. However we are finding that the only way to make the sound work in the plugin is to disable the sound system in Unity. This is clearly undesirable as we may have other environment sounds. Is this an expected restriction? Or is there maybe a way to pass a hook to the Unity FMOD sound system into our plugin?

We are targeting iOS and PC