[a.mik]

Just go to the edit dialog of your sheet file, select the audio tab press the plus button and select the audio file you want to assign. Do the same with the second sheet file. There is no need to import the audio file twice. Hope that is what you are looking for. You could also assign multiple audio files to one sheet file.

Thanks for the hint.
It was my first approach as well. Unfortunately, this doesn't work.

In the audio tab, when I press the plus button, I get a small menu where I can select where to load the file from: Local File - Dropbox - Google Drive - OneDrive
The audio file already sitting in the database cannot be select in that way.

By the way:
Same situation on the Android tablet, with just the small difference, that I can choose from: Local File - Dropbox -Google Drive - System-Filemanager

Remark:
I don't keep the original audio files on the mobile device after having them imported into the database. Would be a waste of storage space on the mobile device.
Those files still sit on my home NAS device.