Ableton Forum

I use an external device (firewire audio) for audio input/output. I frequently shut it off throughout the day. It would be super fab if ableton had an auto-detect feature so that it automatically set to this preferred device instead of having to open up the preferences every time and manually choose it. A simple checkbox that allowed a specific device to be the default would suffice I think.

On macOS you may create Aggregate device which is actually virtual device always connected to your Mac. Assign real output devices to it's chain (in my case two real devices are there: mac's external headphones over builtin 3.5 and external sound card connected over USB).

Assign that device to Ableton's output.

macOS will automatically handle external devices plug/unplug not affecting Ableton's playback.