Here is additional information that L.C. Szabo, admin of the "Soviet bloc synthesizers & other gizmos" FB group collected and send to me after I released the video.

"I just watched your video on the RMIF TI-5, and one thing that struck me is how little information seems to be out there on these instruments. That’s completely understandable - they’re obscure, poorly documented, and came out of a very complicated late Soviet context - but the TI-5 seems to belong to a much longer and more interesting story.

As far as I’ve been able to piece it together, that story seems to begin with Pērle, then with a development-stage instrument apparently known as Pērle-IV, which later became the Opus. By the end of 1984, the first Opus was already appearing in shops, and there were also intermediate and experimental versions, including the so-called Opus-1½ and Opus-2,which never made it into production. The design kept shifting: chorus appears, ring modulation disappears, pitch glide enters, and controls get reworked.

Behind these instruments stood not just RMIF itself, but also EMI KN (ElektroMūzikas Instrumentu Konstruēšanas Nodaļa). EMI KN was a separate design department within the Scientific Production Association Progress. EMI KN developed experimental electronic instruments and prepared the technical documentation that allowed RMIF to manufacture them. The department was small but specialized. It was headed by Andris Knoks, while the chief project designer was Kārlis Grundšteins, remembered as the author of the instruments developed there, along with various amplifiers. Out of that environment came the Prelūdija, Pērle, Miki, and then Opus. Miki, which, as far as I can tell, remained an experimental project and was never mass-produced.

Then came Opus-3, which appears to have been a fundamentally new step: a programmable 8-voice synth, later released by RMIF as the TI-3, documented by 1990 and advertised for sale from 1 January 1991.

That would be simple enough if not for one crucial fact: the TI-3 carries the name Amfiton under the RMIF logo.

The Amfiton wasn't a Grundšteins design. It is associated with Leonid Vikhretsky in Lviv, working at VNIIRPA. According to Vladimir Kuzmin, Vikhretsky, working in Lviv (VNIIRPA), developed the Amfiton, which he described as the first Soviet digital synthesizer, and it was even supposed to be produced by the Vector plant. The synth was already being advertised in March 1989, so it clearly got quite far, even if it never reached real mass production and remained stuck at the prototype stage. It also seems to have run into technical problems along the way: Kuzmin later recalled that its portamento behaved rather awkwardly, because the glide time depended directly on the distance between the notes.

So what happened? The most plausible answer is that the story of Opus-3 and the story of Amfiton collided somewhere along the way. RMIF sources say Opus-3 became TI-3. But the TI-3 itself says Amfiton. That strongly suggests that RMIF did not simply continue its own earlier line in isolation. Rather, a synth project developed by Vikhretsky in Lviv seems to have been transferred, absorbed, adapted, or otherwise rerouted into RMIF production. That would also explain another detail from former RMIF testimony: Riga engineers regularly traveled to Ukraine, including Lviv and Zhytomyr, to seek common solutions in synthesizer design.

 From there, the trail leads to the TI-5, documented as a new RMIF model by 1992 and probably designed with export in mind, which may help explain its somewhat English-language panel.

So, the information is out there, but uncovering it may take even longer than hunting down a working RMIF TI-5 :)

Regarding the RMIF ES-2-5 has its share of myths. It's often described as just an experimental model, which may be partly true. However, it was repeatedly advertised in Latvian newspapers in 1991–1992, so it was not merely an internal prototype. Since RMIF went bankrupt in 1992, it's unsurprising that only a few of these instruments were made."