Well feeling wanting to jump into this discussion of sibilance. I received my Wm1z and have been listening to it with the Vega till 4 am this morning. I also have the LPG Diana edition. Both the LPG and the 1Z have a spectrogram view while the music is playing so one can see the peak frequency at each moments I have been watching for sibilance ever since this discussion is going on. Frankly if sibilance rest at around 7 kHz not that many singers can reach that high. May be with instrument like cymbal but when I particularly choose some soprano pieces for instance Handel Messiah by Dunedin Consort 88.2/24 bit, there are some extremely high female vocal running in a scale and they top out around 3-4 kHz. I have owned the Vega for couple of months now and really have not heard any sibilance once, not on the 380Cu, LPG, or the Wm1Z. I'll be very interested if a reference to the music can be shared so I can listen for myself the incident of sibilance.
At 0:36-0:38
The word 'eyes" was sibilant for me with the Vega and not with U12.
Also at 0:40-0:42
The word "turn" was sibilant for me with the Vega too.
This has pretty much become my preliminary sibilance test.