I got that to work somehow. I use another plugin to clone the event. Than I query the clones, and display their dates. That is not perfect but it works.
The thing with the standard version: First I had problems installing it (http://wordpress.org/support/topic/plugin-all-in-one-event-calendar-hung-up-on-activation?replies=7). After I while I managed it (but I dont really know how), but than I had a conflict with Advanced Custom Fields. As long as the standard version is installed, the fields are not saving. There are other people with the same problems, but I dont know if it has been resolved.
I have to finish this project, so there is no time for experiments, but on the other hand the Pro Version seems to have some features that would be useful if not neccessary for this site. (I say seem, because I couldnt find out weather its true or not) For example, I think in the current pro version it is possible to show multi day events in the agenda view on EVERY day they take place. (For example: There is a workshop starting on Friday, ending on Sunday. I want it to be shown on Friday, Saturday AND Sunday) I read somewhere on the internet, that this is possible. But Im not shure and I didnt get response to my question about that topic. If it is possible in stream view that would be enough.
So: Is that feature included in Standard or Pro?
If yes: Is there any chance to get it to work with Advanced Custom fields?
If yes: How can I install it without deleting dozends of events that are already created with this version?