What you want IINA to do:
Provide a Load External Audio… menu item in the Audio menu under the existing Audio Track menu item.

What IINA does currently:
IINA supplies a Load External Audio Track… button on the AUDIO tab of the quick settings panel.

Why you think this should be added:
To be consitent with how a similar feature for subtitles is handled.

For subtitles IINA provides a Load External Subtitle… menu item under the Subtitles menu as well as a Load Subtitle… button on the SUBTITLES tab of the quick settings panel.