Is it always the same track that you want to mute? One way is to create a group (can be either enabled or disabled) with just that track in it. Then have KM select that track by clicking just to the left of the group name in the Groups Bin, and then have KM type keystroke SHIFT-M.
To have KM know where to click, you can create a variable that defines the screen location coordinates, and have KM click at that screen location. It's a bit of commitment to work like this but if it's something you do a lot/always then it's easily worth it. You'd probably want to set up Window Configurations and make this group one of the first ones in the list to help with consistency between sessions.
Yes, for now I do exactly that... sending mouse clicks to the tracks' output window and "click on mute".
For other macros I click on an found image... but I'd like to get rid of these floating windows and address it directly... "go to track Audio5 and mute it" - or mute 7 tracks at the same time...
While this CAN be done with AppleScript, querying the UI of Pro Tools can be quite slow with AppleScript, especially in larger sessions. So I only do it when it's absolutely the only way to accomplish something.
Here's how I would do it: (assuming you have the preference "Link Track and Edit selection" enabled)
tell application "System Events"
if exists (process "Pro Tools") then
tell process "Pro Tools"
tell (1st window whose title contains "Edit: ")
click button "Mute" of group "audio5 - Audio Track "
end tell
end tell
end if
end tell
These macros will do what you want. They will either Solo, Mute, Input Monitor, Record Enable any track that is currently selected. It will work even if you close the Edit Window and only have the Mix window up. There are two versions; one having apple script click the button, and another with keyboard maestro clicking the button.