Disclaimer: my speculations, not necessarily correct. The tests were done with ASIO4ALL, if you see all other interfaces (non-DAC) measurements they were all done with dedicated ASIO drivers, including M4.
View attachment 112919
M2 also uses ES9016s.
https://prosound.ixbt.com/interfaces/motu-m2.shtml
Even higher-end chips can't achieve this level of steepness
and attenuation.
As well as non-Pro chips:
You can see that the filter really struggled to achieve this level of steepness, which scarifies passband ripple and stopband attenuation.
But the filter shape looks pretty similar to the one on Windows mixer (the third screenshot):
https://www.audiosciencereview.com/...r-mirror-images-short-study.20318/post-674646
Windows mixer is "bad" when compared to something like SoX with 160dB+ attenuation, and when using non-integer resampling ratios, but it is more precise than typical on-chip filters which only use integer ratios. Played through Firefox rather than dedicated audio players to 100% avoid any potential hidden high quality SRC within the player.
That said, I tried ASIO4ALL on the Realtek but cannot reproduce the same result, it is only achievable when playing through Windows mixer. ASIO4ALL's built-in SRC performed pretty poor in my tests.