Have you got the Odroid? How does it compare to the Raspberry 3?
I have both the RP3 and the Odroid C2. The RP3’s architechture is not really ideal for audio duties, as it has a shared controller for USB and ethernet, hence no Gigabit LAN. The Ordoid has separate controller, real Gigabit LAN. Volumio 2, the software on the Ordoid, sound really good. What I like about the Odroid solution is that it has minimal parts count, but the parts are well chosen and well combined. Control is through Bubble UPnP, access to Qobuz etc.
Get NUC running ROCK connected to Singxer SU-1 and you are all set. No need for any kind of streamer in between.
I haven’t tried ROCK, but I am not a big fan of Roon. The interface is cool, but the quality of the metadata for classical is far worse than my own tags. For rock, pop, jazz, blues etc. it’s ok. Also Roon adds a lot of complexity, which has the potential of degrading the sound (continuous scanning of the library, etc.).
I prefer the Odroid solution. It’s a very simple UPnP renderer based on a stripped down Debian base. Minimal processes, very simple. I don’t use the built in Library, but strictly as a renderer and find it works well for me.