If you want to route audio to both the mac and an external device card, you have to create an aggregate device.
More on aggregate devices:
https://support.apple.com/en-us/HT202000"Audio MIDI Setup" help (menu "Help > Audio MIDI Setup Help").
When adding the aggregate device, first select the built-in output so channels 1-2 will be played internally. The external audio card will handle the next channels.
Choose then the combined newly created device as a sound output of the mac.
Finally in QMidi choose channels 3-4 for the click.
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