Can the EXTIO Pin be left unconnected if not used? Or must it be connected to GND through a 0.1uF capacitor. Also, the datasheet does not have any recommendations as far as the bypass capacitor ...

The voltage supplies I am using are ground and -28V to cover the possible range of the input signal. For bypass capacitors, should I just use a bypass cap from the -28V to ground? like a 0.1uf cap?