Are you 100% positive, that the digital filter was the ONLY design change between those DACs ?
Adam your right in where you are going with this from your POV, but as I said it is not just analogue or digital, it is both.
Of course the analogue stage changes in some way (which makes this a pointless debate in many ways) with nearly every product is released but the key point is their digital filter is very different between the two while both measuring pretty much neutral from the analogue output.
If filters all sounded the same then there would not be so many different types, nor concern about pre-post ringing, alias rejection, knee, etc, and technically it is easily shown how they can and do noticably differ in various implementations.
But point in my example, I am not aware of any SS analogue stage that can make a rich/lush sound while maintaining exceptionally low distortion and FR remaining flat (and the digital aspects measured excellent as well) especially when talking about a source product when both use the same chip but very different filter implementations.
There has been quite a bit of work done regarding perception and effect of various filter types/implementations, including anecdotal.
However please note that many digital products when they provide options in reality usually only have 2 that sound different as the rest have subtle different coefficients.
I am yet to see a product that implements a broad range of the different filter concepts because each manufacturer has an idea of what the ideal type is.
Anyway each type of filter concept does affect FR droop, alias rejection, pre-post ringing, knee,etc.
I am not the only one to say each modern DAC chipset has their own sound traits, whether AK, Sabre ESS,etc, especially when using the implemented default option filters.
But to stress, I am saying BOTH digital and analogue stages affect the perception/preference and comes down to design-implementation.
Cheers
Orb