I found the solution. (I didn’t actually solve it in 2 hours – there were a good 16 hours poured into this issue before my post.) Two very important things.
1. Be sure to include the `_inc/ajax.php` file – from the BP default theme – BEFORE the ‘init’ action. The action hook ‘after_setup_theme’ will work.
2. Retain `wp-load.php` as the AJAX url in `global.js`.
After these two steps (and 18 hours of frustratingly trying everything else) it worked like a charm.
