Hi there. Welcome to the forum. I have seen your video.
I think the concept of a digital processor is not understood. The M-scaler has no intelligence. It does the same thing on every input signal. As such, that 1 kHz set of digital samples were modified due to interpolation, dither applied (again), and output over a S/PDIF link which itself can cause timing variations (jitter). So it is very important to run the standardized 1 kHz test. And good thing too because I saw that it substantially degraded the performance of Topping D70s -- something the company does not warn about.
On your #1, DACs internally already upsample to very high frequencies. And provide noise shaping if they want. By your argument I should stop running 1 kHz test for all DACs then. Let's remember that by forcing the DAC to run at higher sample rate, the M-scaler is causing the DAC to operate differently. So it is important to measure its analog performance for that tone as well.
Also, when people make claims of improvements for M-scaler, they don't at all limit it to transients. They may do so after reading Rob Watt's argument but they are not in absence of that.
That aside, Rob provided no evidence that said transient response is a) improved and b) it is audibly beneficial. The word transient is thrown around in audio as standard marketing buzzword. As in that context, it has no meaning.
Let's remember that
a true transient has infinite bandwidth and energy! No way then that it can be contained when sampled with 44.1 kHz which is 99% of what people listen to. Harmonics of any signal over 11 kHz and change is chopped off and gone forever from the format. And even if it weren't, we would not hear it anyway as it is outside of audible range.
It is trivial to improve transient response by increasing bandwidth. But per above, you are reproducing things that you don't hear. And your speakers likely won't reproduce (or distort if they did).
All this said, I did run upsampler specific test in my filter measurements:
There, we again discovered deficiencies in the M-scaler in the way it outputs over its single link. Its attenuation is worse than the naked DAC, something that Rob accepted in your interview but was absence in all prior talk about this device.
All in all,
I found his answers in your interview very disappointing. He starts by saying he has not read my review. Really? He came for an interview on the topic with no knowledge of what I tested? Maybe if he had read the review he would have realized the questions you raised were not valid. Second, he didn't bring any objective measurements, or blind controlled tests to back his claims. So it was just a lot of talk with no reliable evidence.
As a reviewer, you need to be on guard to not be manipulated by a manufacturer with fancy buzzwords and unsupported claims. You started to ask hard questions but then accepted everything he said. That is not right. When he says he has conducted hundreds of even thousands of listening tests, you need to ask him if these were documented in any form so that we could see how valid they are (and try to replicate). At end of one of his talks at an audio show where he repeated his "structured/controlled" listening tests many times, I asked him if his tests were blind. He said no and that blind tests are stressful! Well, they are stressful if there is no difference to be found!
If his answers were too technical, you could have sent me a link to the video in advance of publishing to get my response. But you didn't and published his one-sided response. Before you say my review was also one sided, I provided tons of evidence including listening test samples. He didn't do any of this.
I am happy to see you here so that we can properly answer back. But wish you would put your consumer hat on and defend their interest first and foremost.