macos - OS X: Route audio output to audio input - Ask Different
Set up audio devices in Audio MIDI Setup on Mac - Apple Support
Use the Line In Audio Input on a Mac
Apple iMac 21.5in Quad Core i5-2400s 2.5GHz 16GB 500GB DVDRW WiFi iSight Webcam Bluetooth OS X El Capitan (Renewed) : Amazon.co.uk: Computers & Accessories
Audio In" Port-How do I use it? | MacRumors Forums
How to Output Your Mac's Audio to Two Pairs of Headphones at the Same Time - MacRumors
Changing the Default Audio Format on macOS - Information Technology - UConn Knowledge Base
Use the Line In Audio Input on a Mac
Best way to get audio from iMac to Amplifier | MacRumors Forums