Much of what you hear is not just about the DAC chip in the unit, but also the overall implementation of the architecture/design, which includes the quality of the power supply, the robustness in implementation of the analog output stage, the accuracy of the internal clock, and the isolation across components overall which prevent any interference in the signal which result in jitter and noise.
Digital signals are incredibly sensitive, so from the digital stage the quality of the power supply reduces ripples that induce noise. For the analog stage, they provide the quality current to match the robustness that aftermarket DACs need to provide the body, weight, texture and coherence that your PC won’t.
I’ve also posted on clocking in other threads, but better clocking allows the sample rate to be reproduced with the most amount of accuracy, similar to a photograph taken when the lens is completely in focus vs one where it is just the slightest bit out of focus.
PCs are inherently very noisy - not like white noise noisy but more like jitter (digital noise) which makes audio sound more brittle and fatiguing while being less coherent.