https://support.wix.com/en/article/elements-that-cant-be-added-to-repeaters
Below is a list of elements that cannot be added to a repeater:
All third-party apps
The Pro Gallery
Full-Width galleries
Wix Video
Wix Music
Horizontal and vertical menus
Flash elements
Anchors and anchor menus
Hover box
Repeaters
Box slideshow
The HTML component
Hence why it does not work in the repeater.
Plus, I have just tested it myself in a repeater and the dataset connection does not work through it, so you can assume that Wix Audio Player is classed as Wix Music and so won’t work.
It does work if you put the external URL or the uploaded file in the settings of the Audio Player itself, however as that is in a repeater what you do with the first one will be repeated in all of them.
I even tried doing that myself and it wouldn’t let me, just first three, external url first with the second two being uploaded files, however it still overwrites with the first repeater info.