So here is the tutorial around the Spectrum Wave ICE Node which I used for vimeo.com/41955919. The node and the code is available on github: github.com/claudevervoort-perso/xsi-audio-spectrum
If you try the add on, know it is very beta. If you have issues with it, let me know. I'll see what I can do in the time I have.
Good luck and thanks for watching!