> So you think music from internal SSD sounds better as from Ethernet / NAS?
Yes, no doubt, I compared many times.
> And upsampling of music files to DSD256/512 is also a sonic upgrade?
I am not saying that DSD is better than PCM as a format. However many DACs (like my current one) are more at ease processing DSD and this can be heard. A kind of aristocratic fluidness.
> At least, further sonic upgrade by external (very expensive) clock?
Yes, unmistakable.The RS130’s internal clocks are good but not great. This is of course to be expected as top notch clocks are very expensive and would drive the price up, beyond the reach of many…
> Could you rank, which of the mentioned tasks improve sound quality most?
First local playback, then external Mutec clock. Which is not to say that the latter is an insignificant step up.