I would just like to say that I solved it and made a script to copy/paste on my project blog. The reason I don't post it here is because my script is larger than the character limit.
Here is the summary from my comments in the script:
"// Basic strategy is to call UnityEngine.Microphone.Start(), which begins periodic calls to OnAudioFilterRead in the Unity DSP audio processing thread (“producer thread“)
// and then to call AkAudioInputManager.PostAudioInputEvent(), which begins periodic calls to AudioSamplesDelegate in an AkAudioInputManager background thread (“consumer thread“)
// Microphone input samples are written to a buffer in OnAudioFilterRead (“producer function“)
// and read from the buffer in AudioSamplesDelegate (“consumer function“)
// IMPORTANT: ensure that under Edit –> Project Settings –> Audio, “Disable Unity Audio“ is NOT checked"