There is someone on ebay selling C-9 upgrade kits, also sometimes C-9's with the upgrade installed.
This unit below seems to me much the same thing, but modern implementation, seems you adjust the settings with a computer via USB..
http://www.ambiophonics.org/Ambio4YouDatasheet.html
This unit below seems to me much the same thing, but modern implementation, seems you adjust the settings with a computer via USB..
http://www.ambiophonics.org/Ambio4YouDatasheet.html