With my setup on Raspbian I was unable to listen Ekos sounds. To play them in notification I changed the default play sound with the command ogg123 /path//to/sound.ogg

I just tried your solution but it does not work the same in my case.
I also moved the sound file in the /Applications/KStars.app/Contents/Resources/sounds folder in which all the standard Kstars sound files are located. However, also in this case I am not successful in solving the problem.
The strange thing is that I am able to listen these files by clicking on their icons, or even with the ogg123 command in the terminal.
It's quite weird...
I attach a screenshot of what I've done...

You have to activate the RUN COMMAND and not PLAY SOUND

I just tried also by enabling "PLAY SOUND" and inserting the following command:

ogg123 /Users/angelo/Documents/SuoniNotifche/jinglebells.ogg

exactly as I make in the terminal.

But, after applying and simulating a successful alligment in Ekos, however I've not solved the problem. I look into the notifications window and I noticed that the command I reported above was automatically modified in the following one:

/Applications/ogg123 /Users/angelo/Documents/SuoniNotifche/jinglebells.ogg

it's weird... This should be the reason because your solution does not work in my system.