Okay, got it. Used nircmd + autohotkey combo:
#z::Run nircmd.exe mutesysvolume 1 "Neumann BCM 104" #z UP::Run nircmd.exe mutesysvolume 0 "Neumann BCM 104"
"UP" is a key unpressed event. Key combination here is "Windows+Z".
"Neumann BCM 104" is my device name (as in "Input Devices" in Windows).
Nircmd's mutesysvolume reference: http://nircmd.nirsoft.net/mutesysvolume.html
AutoHotkey's Run reference: http://ahkscript.org/docs/commands/Run.htm