Same issue here with ATH-M40x.
As far as I can understand, it is voluntary option from Steinberg who limited the power consumption of headphone amp enabling more stability and lower consumption on the overall system.
It is not really a big problem because , at long term, exposure to high decibels cause hearing loss especially if we use it for long periods of work ( several houresā¦). It is a very serious issue. 
But I believe that Steinberg can improve for instance it using external DC adapterā¦ 