I didn't think the Intel NUC had an optical out, but your question had me google it, and there may be a minijack/optical out after all. But then there's a next challenge... my Border Patrol DAC is USB-in only. So then I'd need to convert signal to USB (I checked out the Monarchy DIP, and if I'd have sprung for the Border Patrol to have USB + SPDIF output, that would have worked).
At that point, saying 'to heck with it' and just getting a lightweight streamer to connect via ethernet to the network seems potentially simpler.
The iPurifier 3.0 has a done decent job improving the USB out from the NUC, but I'm not really sure how much headroom for improvement of further USB cleanup there is.
I suppose one thing I *could* try though is bring the Auralic Aries w/ LPS down from the main system, and compare the USB-out on that vs. the NUC+iPurifier... and if that trounces the current setup, I'll have proven it's worth doing further improvements.