Midi split cable or midi splitter box? : r/synthesizers
Amazon.com: MIDI Splitter Cable, MIDI 5 Pin DIN Plug Male to 2 DIN Female SmartPhone AUX Headphone Stereo Jack Adapter Y Input Cable for MIDI keyboard, electric piano, synthesizer, MIDI guitar :
DIY MIDI Thru Box, Version 2 – Morocco Dave
MeeBlip cubit duo: USB MIDI interface and MIDI thru | meeblip