To mute FFXI Nasomi when it is in the background, you must edit your Ashita configuration. Nasomi uses the Ashita launcher rather than Windower. Open the Ashita launcher,
CooMeet, right-click your active profile, and select Edit. Look for the Mute on Focus Loss setting within the configuration menu. Enabling this ensures the game stays silent whenever you Alt-Tab to browse the web or watch videos.
If that setting is missing, check your settings.xml file in the Ashita folder. Look for a line regarding "BackgroundAudio" and set its value to 0. This replicates the classic Windower feature you remember,
Uhmegle, allowing you to wait for party invites in peace without overlapping music. It is a quick fix that restores the quiet environment you need for multitasking.