When adding an external sound, using Zone Master, is it possible to mute unmute that sound using a scene?

You can activate and deactivate transmitting via the KBD CTRL feature to that external Zone which will accomplish the same thing. This does assume your external Zone is using one of first 8 Part slots. And you have sorted what each slot is set to Output

Technically speaking, the MUTE buttons are strictly for internal Synth sound reaching the audio outputs. A Mute breaks that connection. But if you created a Zone that is targeting an external device, you can use the Scene Memory’s ability to memorize which Part slots are KBD CTRL active.

You can seamlessly transition from internal sounds and external devices using this method.

From the HOME screen
Touch “Scene” to recall the Scene Memory screen
Along the top are Scenes 1-8, the currently active Scene in bright blue
Turn the Memory switch for “KBD CTRL” = On
Touch “KBD CTRL” the screen will show which of the first 8 Part/Zone slots are currently active.

Slots are active when you place a green KBD CTRL icon there.
Say in Scene 2 you want to turn off communication to Part slot 1 simply deactivate the KBD CTRL icon for its slot and activate the slot you wish to sound

Any changes made on the Scene Memory screen are automatically STORED to Scene Memory.
Remember to [STORE] your User Performance.

That should help… if you get stuck post back here.

Excellent.

Thank you for your assistance 🙂