Primarily the dbx ZC-1 or ZC-6 (momentary push and hold) controller could be assigned to an input gain stage.  On rare occasions, a customer might want to assign a ZC-2 to the input gain.  Normally this is just compatible with the output gain, but there is a work-around.  

The Trick to that is to add a ZC-1 in the software and then Edit the min and max accordingly so that the MUTE switch operates on the ZC-2.  

This can be tricky because the max setting in the edit box does match the dB input gain stage as seen in the software when making adjustments on the ZC-2 Controller.  

ZC-2 Volume Control Edit Window

The ZC-2 may be used in ZC Inputs 1-12. The ZC-2.  Edit window allows the installer to set the Min and Max limits of this volume control from -inf to +20dB.  The ZC-2 may be used as a volume control for inputs or outputs, but the mute button does not mute the input by default (see Note below).  

Note:

When associating a ZC-2 with an input, the ZC-2's rotary control will control the input gain, but the mute button on the ZC-2 will not be functional.  ​This is because there is no mute parameter in the input signal path to be controlled.  To make a ZC-2's mute button operational when controlling input gain, configure a ZC-1 instead of a ZC-2 from the ZC Panel Configuration window (shown below).  Click the Edit button and set the Min Gain parameter to -inf as shown below.  You will then need to associate the controller as you normally would in the Source ZC Association window (don't forget it will now be labelled as a ZC-1).