How to setup multi-channel sounds?

[marplx]

Following your setup with GarageBand, I can only use one track.
I tried to add more than one software instrument tracks in Garageband but all channels e.g. from the "/nickel" project played on the latest created track.
How to support multi-channel sounds?

[marplx]

In https://discussions.apple.com/thread/211900 they say:

Garageband can't route midi, it just listens to ALL inputs it can find and it finds them automatically.

I wonder if I should keep trying with GarageBand.
@dabit Please give me a hint 🙆‍♀️