Your accordion, after having been MIDI’d, becomes a MIDI controller !
This is all beginning to make sense now !
Generally, a MIDI controller doesn’t emit any sound !
The accordion with it’s installed digital interface sends out pure MIDI data that has to be interpreted by the expander.
You can also have specialised Midi controllers like SIPARIO which can connect up to 3 midi devices to up to 3 midi outputs or expanders. In addition, Sipario contains many specialised features for accordions.
The original idea for MIDI in the first place, was to allow musicians to be able to control several electronic instruments from one device.
So, your expander is sitting there waitjing for MIDI messages from the accordion telling it what instrument sound to play !
Bagpipes from the accordion … easy !!