When I work on your demoserver I notice that when I put an event on Private, after registration via CB, you are not redirected to the registration page. You have to go back to the specific event again. This is a pitty ...
Is there a solution for this?
I have not worked with jomsocial - is this maybe a better component?
Neither CB or JomSocial will redirect to any DT Register item... or any other component for that matter. Suggestion would be to use one of the existing 3rd party login redirect plugins... where you can specify a URL to send users automatically after logging in on your site. You could at least redirect to the DT Register listing of events... or to a specific event if you wanted to even.