Hi Matthias,
I'm afraid you don't have 4 playbacks on a CueCore1. This is one of the upgrades in the CueCore2, more playbacks.
You can run multiple (4 to be exact) tracks at the same time though. Perhaps you can work with that?
As soon as a fifth track is played, the first one you started will be stopped. So you would need to stop one via Showcontrol before playing another.
Greetings,
Bootsy