After having a look at the Japanese Stax repair page (with the help of Google Translate), I learned that
Any international inquiry regarding servicing ( / getting parts for?) Stax products must go through the official Stax distributor in one's own country (that was the only piece in English in the whole page, by the way);
The 007 Mk1 can still be serviced by Stax in Japan but with possible substitution of parts. I reckon that in the particular case of the 007 Mk1 this includes the sound elements - they're indeed probably replaced by current Mk2 sound elements.
My email contact with Edifier on my issue wasn't helpful, so yesterday I paid a visit to Edifier's showroom in São Paulo. They agreed to have a look into how to contact Stax to diagnose (a bit moot after one sees the pictures above) and to have a cost estimate on the repair. Let's hope... My impression is that nobody came to them before for this since they started distributing Stax products in Brazil...
There was a good thing that came from that visit already, though: they had a small listening room full of Stax gear, among them the SR-009S, so I could listen to it for the first time. It was powered by the Stax SRM-700T energizer and sourced by the famed (or infamous?) PonoPlayer DAP, spearheaded by Neil Young's PonoMusic until its demise in 2017 (my first time seeing one of those as well).
I've listened to the following tracks, which I had a good memory from listening to them with my 007 rig:
David Bowie, Space Oddity (2015 remaster);
The Doors, The End;
Yes, Hold On;
Glenn Gould, Toccata in E Minor, BWV 914 by Johann Sebastian Bach.
I know I'm about to undertake quite a tricky comparison - I'm actually comparing two completely different audio chains, not just the cans. I'll try to make the best out of it. The comparison will be mostly against the 007A since my Mk1 has been out of commission for a while and I don't trust my impressions so far back in time with enough details to serve that purpose. Even though I had never listened to the PonoPlayer before, I do know it's powered by the Sabre ESS9018K12M DAC, which is inferior to the newer and more powerful ESS9028 PRO DAC in the Fiio X7 MkII DAP, which I do happen to own. Since I can safely say that the Fiio X7 MkII is quite inferior to my RME ADI-2 desktop DAC in every way except perhaps on soundstage rendering, which is somewhat wider on the X7 MkII, I believe I don't need to fear any comparisons on the DAC side (badumtss).
Both cans are very different. The 009S is quite comfortable with the right adjustment on the headband, but you need to find the precise angle to put the headband on for a proper seal. There is also significantly more space for the ears inside the earpad cavities than with the 007A, perhaps even a bit too much (the Mk1 hits the sweet spot in that regard). Regarding sound, the first thing that came to my attention about the 009S was its soundstage - it's significantly wider and deeper than that of the 007 (even the Mk1, I daresay), probably to a large extent due to its earpads. The directional imaging was also superior, seemingly due to the wider perceived soundstage. However, the layering was clearly inferior - there was only "really close" and "quite far" with the 009S, unlike the subtle multilayered imaging of the 007 as already reported by Birgir here on HC. If you take into account the 007's more compressed soundstage (at least in my rig), it only makes that even more impressive. The 009S is ever slightly more resolving than the 007A to my ears, but not sure if that difference is enough to make it more resolving than the Mk1. Instrument separation is comparable, maybe with a slight advantage to the 009S. Regarding bass, there is no contest - the 007 clearly wins, the 009S's bass is just too thin and lacks slam.
The energizer may be also playing a role here - the SRM-700T uses the same tubes I'm using on my T1S (a pair of 6SN7GTB's) but it drives them at a slightly higher output voltage (340V instead of the T1S's 320V) and, more importantly, a higher plate current (each tube section's plate is loaded by a Dale NS-7 1% 7W 47kOhm resistor, which amounts to 7.2mA/section). Increasing the CCS's current to 6mA/section as planned for the near future may improve things on my side. With 4.9mA/section I still think that the Raytheon / Toshiba 6CG7 tubes sound slightly more refined on the T1S, despite the clear improvements on frequency response both at higher and lower volumes with the Tung-Sol NOS 6SN7GTB's.
Regarding timbre, it's a more nuanced matter. I really liked the 009S with solo piano in Glenn Gould's track - the wider soundstage together with that makes for quite a vivid impression of a grand piano in a concert hall, whereas the 007 sounds more like the instrument is in a studio room or perhaps as if you were sitting on the performer's bench. Obviously, it doesn't feel as if you were playing the piano. No sound transducer can convey that feeling - you largely listen to it with your bones through your fingertips, as well as with your ears, as you play. For human voices, though, it's a different story... The 007 is definitely more natural and pleasant. I'd need to listen for more varied tracks and a longer period of time to form a more complete picture of the 009S's timbre against the 007's. That will have to wait for another visit to Edifier's showroom... Hopefully they'll have a SR-X9000 for testing as well by then...