FMOD Studio is a commercial product and standalone tool that provides free licensing to independent developers, which is inline with the Unity license. Since it is a standalone tool, it actually does not need to be used with Unity and in fact is compatible with many other commercial game engines. This is even a more powerful feature if you develop audio assets across game engine platforms. However, the compatibility within Unity with existing tools is another matter.
Unfortunately, as the preceding quote suggests, working with FMOD in Unity uses an entirely different set of components which are incompatible with any of the work we have already covered. Perhaps, in the future, there may be an integration path between FMOD and the Audio Mixer but as of now the audio systems are...
