Seems this is not possible, you can set it to one Button. I tried two. Like this
Joy 7 & Joy 8::
{
Process, Close, {{{StartupEXE}}}
}
But this dos not work, instead it made joy 8 in to the killer key.
this is also mentioned not to work, here:
https://www.autohotkey.com/docs/Hotkeys.htm#combo
You can define a custom combination of two keys (except joystick buttons) by using " & " between them. In the below example, you would hold down Numpad0 then press the second key to trigger the hotkey:
however, wouldn't joy2key work. That way you could set start and select to 2 different (keyboard)keys and then set those two, in combination, to kill the game.