Thanks a lot!!
For anyone who had my problem:
Create a custom field in the post called ‘player’
Set the value with:
[audio:https://www.domain.com/path/to/song.mp3%5D
than place the code below in the place you prefer in the post template (or anywere else)
`<?php $customField = get_post_custom_values(“player”);
if ($customField) insert_audio_player( $customField[0]); ?>
thx again doryphores!