After many years I finally got around to rebuild one of these boxes.
So this old Soviet made device is now a wireless controller that send out OSC. There are in total 34 buttons, 16 knobs and an additional RGB status led. It automatically connects via WiFi to MaxMSP or SuperCollider and run on 5V (USB powerbank).
KiCad schematics, Arduino firmware, SuperCollider classes and MaxMSP abstractions attached below.
The inside is quite a mess. I use an ATmega168 together with six 4051 multiplexers to read all the inputs. the WiFi module is an ESP8266-01.
update 190124: v1.1 fixed a small but breaking bug in the ATmega168 code.