What your ears hear depends on the electrical signal. We can measure that VERY precisely. Far more precisely then your ears can hear. Also what you hear is the result of loudspeaker frequency response alterations and phase changes and room reflections etc which will dwarf electrical signal distortion from a DAC by several orders of magnitude.
This just highlights why subjective listing does not work for DACs - you really must volume match by matching the electrical signal voltage from the DAC outputs and blind test.
While it's true that electrical signals, loudspeaker frequency response, phase changes, and room reflections can influence what we hear, there are a few counterpoints to consider regarding the claim that subjective listening for DACs doesn't work.
Human hearing is more complex than just an electrical signal. While we can measure electrical signals with extreme precision, the human auditory system doesn't work in a purely mechanical way. The ear-brain system is sophisticated and can perceive subtle differences in sound quality even if they aren't immediately measurable by the electrical signal alone.
While room acoustics, speakers, and reflections certainly play a huge role in shaping what we hear, they don't necessarily "dwarf" the influence of a DAC. High-end DACs are engineered to minimize distortion, noise, and colorations. Even minute distortion from a DAC can affect the perceived sound, especially with high-resolution recordings, where you might notice finer details that a low-quality DAC could obscure. So, in some contexts, DACs can make a tangible difference in sound quality.
Volume matching and blind testing are useful, but they don't account for all perceptible differences. It's true that volume matching is critical for any blind test, as louder sounds can be perceived as better, but subjective listening doesn't need to be reduced to just blind tests. People can still identify preferences based on tonal characteristics, dynamics, and other subjective criteria that might not be measurable with traditional equipment. Some of these nuances may be more obvious in a more controlled listening environment.
The idea that subjective listening doesn't "work" because of measurement and blind testing doesn’t account for the fact that audio is a personal, emotional experience. What we hear and how we react to sound involves more than just measurements ~ it’s about the emotional connection to the music. This is why subjective listening can often reveal preferences and qualities that raw measurements alone can’t predict!