How to do live monitoring of audio input on Mac? (i.e. hear the input sound on audio out)
Is there a generic way to do this or is is application specific?
Audio monitoring is application dependent.
For example, when using Ableton Live all you have to do is to set up a channel using EXT.IN (or whatever input your using) and change the the monitoring from AUTO to ON.
Most application will have you change the monitoring of a specific channel to on - some of them you'll just need to 'arm' the track, which basically means clicking on the record button of the channel you want to monitor.
Using internal system audio routing for monitoring is not recommended since it's relevant to be able to control the channel's volume while monitoring.
I don't know what software you're using but it's possible to use Audacity on a Mac - there's specific instructions to enable audio monitor here.