1. First of all you need the "Master Volume Docklet" by fedroponce: https://www.wincustomize.com/explore/objectdock/14589/

2. Put the icons folder in "C:\Program Files (x86)\Stardock\ObjectDockPlus2\Docklets\MasterVolume".

3. Right click the dock and select Add -> Docklets -> Master Volume.

4. Right click on the Volume docklet -> Volume Docklet Settings -> and select "Master Volume icons by sharp-design" for the Image Set. You can also disable all "Docklet Info"s.