So I've done some more focused listening with my ZX500 + XM5 LDAC with DSEE Extreme on.
Straight off the bat, for some reason DSEE Extreme works like expected on my Walkman, but not on my android phone. On the ZX500 the DSEE function turns on during CD quality music as advertised, but the only way I've been able to have DSEE work on android is if I use a lower bit-rate codec.
That aside, I have to say I'm beginning to become a believer! I can actually hear a difference in sound when enabling it even on good quality music, the bass becomes tighter and not as flabby (even with EQ), voices seem to be
"clearer" and more present, things like Violins and flutes also come off as more clear and present, with the DSEE function turned off they sort of "fall" behind and mush a bit closer together. The effect is subtle, but there clearly is a difference I am able to pick up. From my limited testing I actually like the effect, it definitely makes the music sound more "clear" and dynamic even if it's by a small margin.
I also have an easier time focusing on voices and their nuances with DSEE Extreme on, turning it off I notice the mid bass bleed over those little details and they get lost in the mix more.
I would recommend experimenting with this, if your device can properly utilize it and work with LDAC.