Well it could be the good old law of diminishing marginal utility... maybe with really high end headphones the role of the DAC diminishes, as the inherent sound quality of the headphones are so good... All my experiences are essentially with speakers.. I have only 1 headphone... Who knows.. The test itself concluded in the end saying that differences may happen in speakers they can't say... I wonder if they wanted to conclude this spectacular finding that 2 USD vs 3000 is the same and a speaker test would have come in the way