Steve,
Although I am sure a Nucleus+ would be better (I’m waiting to try one), the configuration you are describing is almost exactly the same as one I have been running for a while. I use the same Qnap for 350k tracks and since it settled down (which took a few weeks of analysis etc) it has been very reliable. I don’t have need to reboot Qnap (current uptime 101 days).
Having said that, it depends I imagine on what else you are asking it to do. Although I use several endpoints, I never request signal processing on the Qnap - I suspect that would stress it out.
My interest in the Nucleus+ is faster focussing.
The image below shows the resource usage on Qnap.
I was prompted to answer you about the Ultradac. In my experience the Sooloos network endpoints will always give a better sound than a USB connection, especially from a PC or Qnap. At this level of performance everything makes a difference, including cables, router etc.
Danny is right that having the analogue audio parts well away from ‘radio noisy’ networking is a good idea.