The differences are measurable, but not audible. You need to do the test blind (with help of a third person) to realize that you can't reliably tell one from the other.

Technically you got it all correct. 'Factor 1' is the ideal for a SRC, minimizing all kinds of noise and distortion. I measured both ways so you can see the difference, SPDIF Slave direct and through SRC. The result at the analog output is limited by the DAC, of course, and there is zero difference, as the SRC itself clearly outperforms the DA conversion.

(For the geeks: the analog output measurement has been done with an active notch filter into the input of an ADI-2 Pro. It won't get better no matter how much money you spend on an Analyser

You might say Noise and Distortion are just two of more parameters to check. Let's have a look at the frequency response and phase shift. I used an old tool called HolmImpulse, but one could also use REW to do the same (both are free). The pic shows the expected outcome. The SRC has (must have) a self-adjusting digital filter, but it is steep and usually doesn't influence the frequency response in a negative way. One can see a very small drop above 20 kHz. The phase shift is ridiculously low (DAC filters usually cause much higher values) and stays below 10° up to 20 kHz. None of this is audible.

To better see the details here is a bigger version:

https://archiv.rme-audio.de/images/holm … _large.png

Of course there is much more to see/measure when the SRC has work to do (no 1:1 ratio).