It has been almost two months since I received the speakers, and I estimate that I have used them for close to 300 hours. Last night, I had the pleasure of having two S3MK2 owners visit my home. Both of them use Luxman 900 pre- and amps (similar to my electronics), and both of them are very familiar with my system, meaning they have heard the S3MK2 in my room several times.
We all sat down and I let them play the music they know well. Their reactions were as follows:
(a) The new speakers have a much bigger soundstage than the previous generation.
(b) The new speakers are much more airy and detailed in the upper octaves, able to reveal more details than had been possible on the previous S3. The new model is able to do this without the cost of being a bright speaker.
(c) The mids are more detailed, perhaps a little less "sweet" than the previous model, but more coherent with the tweeter. Both of them preferred the current female and male vocals or instrument voices that the new S3 throws into space.
(d) In the lower octave (bass), the S3MK3 is more detailed and can move more air, and the sound is deeper than the S3MK2 can achieve.
In addition to all of the above, you can add that there is less box resonance (just put your hand on the older and newer S3 when playing a low octave). The new speaker is also very agile and quick.
To summarize, the new S3MK3 speakers are a significant improvement over the previous generation in terms of soundstage, detail, clarity, and bass performance. They are also more coherent and agile.
Last, I think the new model design feet and finish are beautiful and better than ever.