If you run the standalone app and don't get any audio output from your interface, the root cause is likely that your Mac is not allowing Metallurgy to use its mic.
During the installation or upon launch of the Metallurgy standalone app, if prompted to allow Metallurgy to access the computers microphone, click OK. You can also manually edit this setting within the Macs System Preferences > Security & Privacy > Privacy tab - Microphone settings.