Thank you JAC!, Well in Atari800MacX on a Mac it looks like this:
Bildschirmfoto 2018-06-15 um 00.45.01.jpg
On the other hand, on Altirra on Mac (published before), it works like a charm!
=> we have to trash the beloved emulator for the Mac and must switch to Altirra. It seems, there are more problems with that emulator then just the missing sound.
Wade will compile a new version for Atari800MacX in the future, until to that point Altirra is without any alternative.
Thank you very much JAC! Big sorry for the trouble, but I think, we have discovered here a ground based problem.
Can't say very little about A8-bit emus on Mac... but on PC-platform, it now seems unlikely we will ever see anything more complete or as comprehensive as Altirra....
Altirra has gone and reached places prior attempts have only dreamed of... And that is a fact!