AppleScript that switches audio, toggling between display and AMP / DAC

toggle_audio_output.scpt

tell application "System Preferences"
	activate
	set current pane to pane "com.apple.preference.sound"
end tell

tell application "System Events"
	tell application process "System Preferences"
		tell tab group 1 of window "Sound"
			delay 1
			click radio button "Output"
			if (selected of row 4 of table 1 of scroll area 1) then
				set selected of row 3 of table 1 of scroll area 1 to true
				set deviceselected to "Display Audio"
			else
				set selected of row 4 of table 1 of scroll area 1 to true
				set deviceselected to "FiiO USB DAC-E10"
			end if
		end tell
	end tell
end tell

tell application "System Preferences"
	quit
end tell

tell application "Growl"
	set the allNotificationsList to {"Sound Notification"}
	set the enabledNotificationsList to {"Sound Notification"}
	
	register as application "Toggle Sound Output" all notifications allNotificationsList default notifications enabledNotificationsList icon of application "Script Editor"
	
	notify with name "Sound Notification" title "Audio Output" description deviceselected application name "Toggle Sound Output"
end tell

See alternative command-line utility switchaudio-osx:
$ brew install switchaudio-osx

$ switchaudiosource -s "FiiO USB DAC-E10"
$ switchaudiosource -s "Display Audio"