I'm not sure what you're trying to do vís-a-vís MainStage 3 and something called iPadian Setup..?
MainStage is a macOS application -- it runs on Macs (usually some kind of macBook, for live work), and if you have macOS 10.12 or later you can buy/download/install it from the Mac App Store.
I don't know what iPadian Setup is -- apparently there's a piece of software called iPadian which seems to be an iPad simulation (not a fully-functional emulator) for Windows (and Mac?). I came across numerous warnings of malware & adware in this iPadian, so I'd suggest you proceed with caution. If that's what you have there, honestly, going by the scant but mostly negative information I found, I'd deinstall it and steer clear..