ESD protection diodes on audio inputs / outputs?
If not, where would be the best place to place the diodes?


If on inputs internal protection diodes could be placed right after the connector, or a series resistor on the input and protection diodes. Depending on the signals, series resistors can be placed between the input and the amplifier. Most amplifiers have internal protection diodes, however, these diodes cannot dissipate a lot of power. It then becomes necessary to use external diodes if the input signal could go beyond the ratings of the internal protection diodes. The max rating for the AD8655 is 3kV for the human body model of ESD. 


  AD8655/AD8656 Data Sheet pg16
  INFORMATIONINPUT OVERVOLTAGE PROTECTION 
  
  The internal protective circuitry of the AD8655/AD8656 allows voltages
  exceeding the supply to be applied at the input. It is recommended,
  however, not to apply voltages that exceed the supplies by more than
  0.3 V at either input of the amplifier. 
  
  If a higher input voltage is applied, series resistors should be used
  to limit the current flowing into the inputs. The input current should
  be limited to less than 5 mA.The extremely low input bias current
  allows the use of larger resistors, which allows the user to apply
  higher voltages at the inputs. 
  
  The use of these resistors adds thermal noise, which contributes to
  the overall output voltage noise of the amplifier. For example, a 10
  kΩ resistor has less than 12.6 nV/√Hz of thermal noise and less than
  10 nV of error voltage at room temperature.