Thanks to all for your recommendations.
You helped me a lot.
I am not really good with screwdrivers or checking out individual settings (like NUC with Rock). I want/need an easy to use solution.
It sounds to me that this will be the Nucleus (but a very expensive one).
I think my NAS (DS218 play Synology 8.8 TB) should not be the problem.
The NAS is directly connected to my core (Mac mini) via one Netgear switch (so that should also not be the problem.
I am using Qobuz (that information is for Bill).
All looks like a performance problem with my older Mac mini.
I do have some additional questions:
So when I buy a Nucleus now, will the music files still remain on the NAS (8,8 TB Music files)?
Is it easy to transfer the library, playlist, settings etc. from the Mac mini to the Nucleus?
Which nucleus model would you recommend to me (the expensive one or the very, very expensive one)