Regarding DACs and hearing differences—i am no where near your skill. I would agree with your statement that it is to “do with implementation”.
To be clear, I fully agree, that it is theoretically true about the importance of "implementation", but in practice?? The chance for a manufacturer to use a top notch expensive DAC IC, to not implement it properly, or more than good enough to take advantage of the chip, is every slim. That is not to say it never happened, but I think most of such talks could be largely due to the following:
a) excuse (easy to do by any) manufacturers used to justify their use of lower spec DAC ICs.
b) as above, we often other similar excuses, such as "it doesn't matter which IC, all but the cheapest DAC ICs are sonically transparent anyway..
c) as a), b) or other reasons not listed, via hearsay from print magazines and now the internet, that keep re-forcing such talks, so now there are tons of people just repeating the same myth (okay, call in semi myth as they might still be some truth to it in some specific cases) that it is not the IC itself that is important, but the implementation.
Another reality to consider is, one can easily google the topic, the fact that manufacturers (e.g. TI for sure) often provide evaluation boards, similar to that on the power amp side such as Hypex, Purifi and others, such that DAC, AVR, AVP, Integrated amps don't even have to do their own design unless they want to custom design their own for their own reasons/applications.
I would like to suggest that we, on ASR, science based forum, to stopping helping manufacturers to find excuse for not using the higher model DAC ICs (doesn't need to the the top model such as the ES9038, or AK4499, but how many the mid range models such as the ES9018, AK4493, 4497, or TI's PCM1795, 1796 etc., and "implement" them well enough by at least doing it to the DAC manufacturers, i.e. ESS, TI, AKM, Cirrus Logic/Wolfson's standards/recommendations.
DAC manufacturers have vested interest to help audio devices manufacturers to implement their chips properly for their own benefits, and obviously, reputation.
Take a look:
Please download from this page for details of the sound solution demonstration board developed by combining our best-performing DSP and flagship DAC.
www.akm.com
Don't we find that look similar to Denon, Marantz's own DAC boards, in their marketing info?
Evaluation Boards specifically to analyse the audio performance of ESS Audio chips. ESS Evaluation Boards from ismosys.com
ismosys.com