Each speaker has its own device which consists of a NodeMCU ESP8266 and X9C104 digital potentiometer inside ... how this should work: The X9C104 is a 100kOhm E-POT (1kOhm steps), with max. 4mA of ...

As usual I’ll be using a NodeMCU board (I really did order a lot of them) which uses an ESP8266, but there’s no reason this would be difficult to achieve on an Arduino-based device.