Interesting. Yeah, AHK is pretty powerful. I'm using it now in the jukebox build I'm working on to independently track 3 mice and make each control something different (the mouse wheels will be connected mechanically to knobs on the cabinet).
Anyway, from the docs on the site....
$
This is usually only necessary if the script uses the Send command to send the keys that comprise the hotkey itself, which might otherwise cause it to trigger itself. The exact behavior of the $ prefix varies depending on operating system:
On Windows NT4/2k/XP or later: The $ prefix forces the keyboard hook to be used to implement this hotkey, which as a side-effect prevents the Send command from triggering it. The $ prefix is equivalent to having specified #UseHook somewhere above the definition of this hotkey.
On Windows 95/98/Me: The hotkey is disabled during the execution of its thread and re-enabled afterward. As a side-effect, if #MaxThreadsPerHotkey is set higher than 1, it will behave as though set to 1 for such hotkeys.
So, since you want to send the Joy8 input in response to the same joy8 input, you'd need to use this to prevent the hotkey from triggering itself.
I didn't know about this trick...