Disabling volume control for USB device that has hardwired volume knob?

This is kind of opposite of what many people were asking over the years.

I've USB DAC / headphone amplifier. It has its own (hard wired) volume control. However, the host (OS X) also allows me to control volume from the keyboard. This effectively results in dual independent volume control, which I find to be very annoying feature. Because the output volume is now a function of two completely independent volume controls, on the host side (OS X, controlled via keyboard) and on the amplifier side (controlled by hard wired volume knob with hard stops). If I set volume on the amplifier to e.g. 25%, the actual volume can be very quiet or very loud, depending what the other volume control (on the host side) is set to. And vice versa. Dual independent volume control is something you generally want to avoid in audio setup, so I'm looking if there's some way to disable it on the Mac side (OS X), and have it simply send the "digital version of line-out" down USB to the DAC / amplifier, and let amplifier be the sole controller of the output volume.

I've actually two of these DAC / headphone amplifiers, FiiO E10K and NuForce µDAC2. And same problem with both.