If you want to have getting on for two hundred keyboard shortcuts (something people apparently do want to have, though I'd bet no one person has memorized a fraction of the lot), some of them are going to have to use modifier key combinations.
Over here the Zoom keyboard shortcuts are Cmd-minus (-) and Cmd-equals (=) for Out and In, but you appear to be in Windowsland. Perhaps the ctrl-key equivalents are already taken by the OS?
Anyway, Max can only map keystrokes based on what the OS is feeding it. One would have thought that the ASCII codes generated by your numeric keypad would be the straightforward Plus and Minus chars, but sometimes OSs do strange things with numkeypads. If you open up the help patch for [key], does it tell you anything helpful when you hit these keys?