Currently in the plugin I do not have an On Audio End event however our api does have one available and I will work to get the code updated for you tomorrow.
Right now the Start Audio action which has the event available only allows one file to be played at a time while the Play Sound action can play multiple files but has no On End event available.
I talked with our native developers about enhancing the audio api to give give functionality like start/stop/monitor multiple audio files at once,as well some other cool features. That will probably take several weeks to start, implement, test, deploy given the current priority list.
I hope that helps.