PC or Nuc? running Roon core

No. That’s not what I said. Please re-read my post.
Besides, I don’t even know what you mean by 

I have an old Intel Dell PC in another room running ROON OS. It’s networked via coax to my Gustard r26

How? You have a coax cable from your PC into Gustard? Or you have Ethernet cable into Gustard? 
 

USB with a proper streamer is a high performance and high resolution interface. I even gave you a suggestion for a good streamer. 

erik_squires,  Thank you for your suggestions. 

audphile1. I had roon streamed into a Upgraded Node, connected coax to my Gustard DAC and liked the direct to Gustard sound better. Increased soundstage, ect. But your suggesting going back to a better streamer for best results?  Doesn't the usb cable connect subtract from the sq?

Gentlemen: What do you think of a roon nucleus one or nucleus as alternative to the NUC?

I really like the idea of going with tiny, low power (i.e. efficient) computers. I do often worry about the noise a wall wart or PC power supply can introduce.  If you want to do an all-in-one, consider an NUC you can get a linear power supply for AND get a medical grade isolator for the USB.  It's not always necessary to use, but it's remarkable some DAC makers still don't isolate the USB inputs fully.

You can keep the Roon Core on 24/7 in another room away from your system. Ethernet connection to Gustard will most likely sound better than USB from a noisy PC or Nuc. In addition, if Nuc is not fanless you will hear the fan while listening to music. 
If I were you I would pick up a used Lumin U1 Mini and use it as a roon endpoint via USB into gustard with roon core in another room.