It has been commented on by many reviewers as the weakness of these speakers, 3.5mm first goes through ADC that converts into digital signal, goes through a DSP, and then through the DAC, which converts back to analog signal again. All sounds must go through the DSP, analog or digital.
Maybe to cut down the manufacturing cost, the speakers is only using a digital pre-amp and volume control is done digitally. So that's why the analog signal has to be converted to digital first with the ADC.