I heard S1 as bassier, warmer and more musical. W2 is more neutral and analytical. Staging and noise floor is where I felt W2 surpassed S1, but S1 is no slouch in that regard either.
I personally preferred W2 but either is great.
The thing that irritated me with S1 is that I could hear a slight hiss with my campfire IEM’s, and I didn’t like the large volume steps. Also when switching from FLAC to MQA tracks on Tidal, I would get a loud popping sound that would pierce my ears. Another issue with S1 was EFI.