Define the actual listening task
List the physical outputs you intend to use and whether they are connected and working individually. Apple’s Audio Devices window distinguishes multi-output and aggregate functions. Choose the feature that matches your task rather than treating both names as interchangeable ways to make sound louder.
An illustrative requirement might be to hear a permitted video through two selected local outputs. Start with a modest listening level on each. Check whether this is appropriate in the room, since sending audio through another speaker can disturb somebody who expected only headphones to be active.
Build a named output group
Apple documents creating a Multi-Output Device with the Add control in Audio MIDI Setup, selecting the included devices and choosing a Primary Device. Give the new group a descriptive name that identifies the intended endpoints. Use the actual devices listed on your Mac.
Before selecting it for normal listening, verify that each endpoint plays a familiar sample on its own. Then test the group and note which outputs are audible. A new group appearing in a sidebar is configuration evidence, not proof that both amplifiers, cables and volume controls are ready.
Compare the listening result
Listen for unexpected silence, duplicated room sound or an unsuitable timing relationship. Do not promise that a multi-output group creates a synchronised whole-home system or a surround mix. Its usefulness depends on the chosen devices and the listening task.
Keep the original single-output choice available so you can return to a simple baseline. If asking for support, provide the Mac version, group members, primary device and the specific endpoint that fails. Remove unused groups deliberately to avoid later selecting an old configuration whose hardware is no longer connected.