I finally got the Raspberry Pi to talk to the ER-301. Almost directly from the Pi to the Sound Computer. “Almost”, because it requires the use of i2c-gpio aka. “software i2c” (capable of handling “clock stretching” - wether the 301 uses this tech or not, it might be useful for other modules - and giving the possibility to use external pull-up resistors of 4.7k instead of the 1.8k present on the regular i2c circuit of the PI. (It’s a common value and is the one recommended in the manual of the Olimex board.)
This seems to prevent the ER-301 from failing when it boots up.
I will now continue to work on the Node.js side of the project and implement all the commands available for the Er-301 (Tr.pulse, Cv, etc).