In your case, wouldn't it be easier to use something like
this and change the commands to use the WinKey aswell? I think remapping the scroll event with pressing [+] and [-] is a bad idea and breaks scrolling entirely, even if you don't use the magnifier.
Otherwise, wouldn't {LWINDOWN} and {LWINUP} or {RWINDOWN} and {RWINUP} be the Windows key?