Are you asking why there's still some sound when the volume knob is all the way down, or are you saying that the volume is too loud at any point?
If it's the first, Cliff said he did that on purpose to prevent people from thinking their unit was broken, when in reality they hadn't turned the volume up. Don't ask me to find the quote, it's been a while and I don't know where to look.
If it's the second, if you're using factory presets, then turn the volume down on your monitoring device. For example, I use CCA C10S IEMs, and using factory presets as my baseline volume, I have the output 1 knob less than a quarter of the way. When listening through my Scarlett 2i2 and Audio Technica M20X somethings, plus a corrective EQ patch lowering the gain by 5 or so dB, I have the volume at just above a quarter. It doesn't take much to drive headphones.