OnAudioFilterRead on a mixer group?

I thought with the new audio system it would be possible to write audio effects and place them on mixer groups. However, I am finding that when I create a script that implements OnAudioFilterRead, I am not able to get it to attach to anything in the mixer (only to an object with an audio listener). The documentation is just a bit vague here. Do I need to inherit from something specific to get this functionality?

 

Was seeking this out today too. Add the script that references OnAudioFilterRead() to the object with the AudioListener, most likely the camera, to get data from the final mix.

 

I know this is a super old thread but did you find a solution to this?
I want to get the audio from one mixer group, and not just a single audio clip or the master audio.