@jrapp Qobuz works with my NUC running Roon but not Aurender, so it's a Aurender problem.
The basic conclusion I am taking from all of this is that there isn't a very big difference between an Intel NUC and a dedicated music server. It is approximately equal to upgrading an USB cable, if that.
Better to spend money on upgrading cables, DACs, Amps, etc etc, than spending 1000s on a music server.
There was a review on Computer Audiophile on the Grimm Music server MU1 where the reviewer (THE reviewer) says he heard no difference in USB outputs of the 10000 euro Grimm server and his NUC.
So while I agree, better USB/clock etc in a dedicated server might make a difference, it is not a lot and certainly the price/performance upgrade ratio seems low.
Crux of the story: I bought a lifetime licence of Roon and sticking to Intel NUC for the time being and keeping the $12000 (price of Aurender N20) for future upgrade on cables or a Shindo preamp :)