Howard,
JFBConnect creates standard Joomla users. I'm not familiar with the implementation details of AcyMailing, but it will probably have it's own additional user table that you will need to insert a row into for the user. This would be done in the Social Profiles plugin you're planning on creating, with the 'createUser' method. In general, it could be a simple insert into the table or calling an API method on AcyMailing.
If JFBConnect detected that Kunena was installed on your site during installation, it will have placed the files in the /plugins/socialprofiles/kunena/ directory. Otherwise, if you unzip your JFBConnect installation package, you will find the plugin package file in /packages/plugins/socialprofiles/kunena.zip
If you look at the code for the Kunena social profiles, there are really only about 6 methods that you will have to update and the link you provided gives descriptions on what each one of them does. We've structured and written the profile plugins to be as simple as possible to create just using that steps defined at the link, but if you run into any difficulties please let us know and Alex or I can help you out.
-Melissa
Creating a Profile Plugin
