What is your Main Stage version? I have MainSTage 2 - did you just download MainStage 3? Then I cannot help with that.
I never actually used MainStage 2 for anything, I just bought it as JamPack installer.
To get started,
- click the MainStage icon in the Dock or Applications folder.
- Then go to the main application menu: MainStage > Download additional content and select to install all uninstalled:
To actually use MainStage, connect a guitar, keyboard, or microphone and click the QuickStart tab.
I don't think I'll use MainStage but wanted to learn more. I have MainStage 2 also.
I had found MS easy enough in my apps. When I opened it I went to MainStage at top as you showed. But mine doesn't show "Download Additonal Content " like your snap shot does. Also "Open Apogee Control Panel" and "Audio Unit Manger " are grey not black. So hitting does nothing. I also plugged my keyboard up to see if that changed anything. It didn't . Still looks the same.