Thank you for your lightning quick impressions, which further heightens my desire to get a pair of EX800sts.
I will elaborate further.
The EX800ST has two main issues: one can be fixed with EQ and for the other one you'll have to live with it.
If you see some graphs around you'll notice this massive peak around 5.4kHz, this is not only very noticeable when you use a tone generator, but also when you listen to music. It gets even worse for a lot of people as some have a natural 5kHz resonance peak for shallow inserts.
The result of this is that the overall timbre is completely destroyed. Dave Brubeck's piano for example goes from energetic and dynamic to downright annoying to listen to. The drum is even worse, because some hits sound as if they explode right inside your brain, while others, due to its ridiculously large soundstage sounds way too further apart. The result is this uncanny feeling that there is more than one drum kit on the stage. This problem actually happens a lot with a lot of measurebait ChiFi sets, but it's sad to see Sony making this mistake in a supposedly professional tool.
The other problem is the lack of treble extension. It makes things like the E5000 sound bright in comparison. It's also unfixable with EQ. I've tried. Better to just leave it as is or apply a conservative high shelf, but you won't get there to the level of HiFi sets trust me. Now, I'd rather have no treble over bad treble, but it's still not good for 2024 standards.
The good? Overall the tuning is agreeable, old school, perfect for instrumental tracks. It has a dip on the mids that contributes to the large soundstage, and coupled with the fact that it has a huge vent making it essentially "open back", gives it the largest soundstage I've heard. It has zero isolation though and leaks like crazy so RIP privacy and your hearing, and also the bass is gone whenever you step out. Unusable outside.
The bass is among the best I've heard... you know how in some cheap dynamic drivers you have to manually roll off the infra as they start distorting like crazy and that distortion carries over the audible bass region? Yeah it does not happen here, not needed, and because of that it has one of the best bass textures out there. if you like cellos and double bass you'll enjoy a very good reproduction here, and it doesn't turn into a mess when a track gets busy.
I think the author moved on to work on the JustEar IEMs as he considered the DD tech can't get any better. They're actually very polarizing, just like the EX800ST and EX1000. For Sony stuff, honestly better stick to Eiji Kuwahara's work. The Z1R is everything the EX800ST wants to be and more. The IE900 is also inspired by the same tuning and fixes its tuning issues.