Just for interest I had a look at the contents of the EEPROM which holds the config for the CM6400. Using an Arduino UNO and a small sketch from Adafruit to read the EEPROM and send to the PC via Serial. The result looks like this. 

ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff

ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff 4d

ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff

ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff 4d

ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff

ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff 4d

ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff

ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff 4d

ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff

ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff 4d

ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff

ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff 4d

ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff

ff ff ff 

 I was expecting more. Maybe my code for reading the EEPROM is not right Ive never read an EEPROM before so possible issues in the Arduino sketch may be to blame. I might come back to this later.

In order to read the EEPROM I lifted the SDA AND SCL lines of the EEPROM and noted when trying the mic out it still connected happily to the PC and audio out worked fine but noted that the mic through to headphones with in the Blue Yeti no longer worked. The Mic shows up as a generic USB Audio device rather than a blue Yeti as expected and the PID is also different.