I was able to listen to the Plenue S fairly extensively thanks to a helpful shop (Minidisc), and I did enjoy the sound, though the price is bit beyond my reach.
It sounds "nice" with good vibrant focus on the main instruments, without being too monitor-like or full bodied. Imaging is a bit more focused and not as thick as AK240, while not as airy as the X7. I really enjoyed listening to it.
I think it would be silly to say which one is "better" since they all have character, so it's best to audition them and pick the one that has the most enjoyable personality (it's like buying a supercar).
I thought the major issue is the price. Fundamentally it's a no-frills Plenue 1 with balanced out and native DSD, so this should have been a direct update of Plenue 1 at a similar price point (considering Plenue 1 is getting a bit old). I'd hate to think that the "2nd Gen" Plenue 1 (if it ever comes out) will have cut-down specs just to differentiate it from Plenue S (Just like how AK320 removed native DSD simply to differentiate from AK380).
I did a quick measurement and the output was definitely more powerful than the Plenue 1, and agrees exactly with the spec 3Vrms = 8.5Vp-p. Turning the "Headphone Mode" off in the menu simply capped the max volume to 1.9Vrms.
Unfortunately I couldn't try the balanced out, since it was a 3.5mm 4-pin arrangement. Manual says it's (starting from the tip) [L+ R+ L- R-], so I guess any Oppo or Sony "ground separation" 3.5mm cable would work, but it's totally different to the AK's 2.5mm pin arrangement.
One strange thing I noticed was that the USB DAC mode was a bit dodgy. Somehow 88.2 and 176.4kHz were grayed out (on Mac) and Audirvana or JRiver often lost connection or downsampled to 44.1kHz. Maybe later firmware will fix this. Optical out could do 192kHz but DSD was silent. Playing 352.8kHz file would downsample to 176.4kHz so that worked fine.