The common thing with all the people doing NOS dac is that the digital filters is the main problem, it seems. Removing the filter function results in better SQ hearing wise.
Going back to Peter, he talks about frequency and time domain and feels that not a lot of thoughts/effort has gone into the timing side of things, which ties in with Opus's thing with CM distortion. Lately I have also find that phase and polarity does affect SQ to a large degree but it is a subject that most people dismiss or ignore.
Your last statement is intriguing to a non-techie (me) in that the Zanden NOS DAC made a big point about no digital filter, but also about its emphasis on phase linearity which Yamada San felt was quite important (he also has a polarity switch as one of 3 main knobs on the DAC). Are these 2 the same as far as you know as to what you were describing in your post? (dont want to confuse terminology). If yes, can you share more of your observations about what makes these 2 elements (Phase and Polarity) important to you in digital?