Roon Nucleus

Think of it as an OS, an operating system, much like MAC OS, Linux. and Windows. Roon wants to be the audiophile OS and control everything, and as as business model this makes sense. Will it be "audiophile" grade and successful, well who knows, I suspect you will get multiple opinions. I have been using Auralic Aries Lightning DS connected to my NAS (via Minim Server) and steaming to my DAC for years, so what do I know. I listen to analog almost exclusively anyway (tape and vinyl).

I ditched analog completely but that’s another discussion...I have been using Bluesound for the past 2 years, Node and Vault, but have found it almost as buggy as iTunes on a PC, and the Blue OS App is nothing special, essentially mimicking iTunes.  With all the Bluesound crashes I began to realize that storing my CDs in a proprietary HD was a problem.  Much better to have them on a NAS and then I could pick the playback mechanism, etc.
  So Bought a Synology NAS and was able to transfer the Vault contents to that and have resumed ripping CDs.  Since Roon is the flavor of the month I tried the free download.  It took forever for Roon to scan the 800 CDs on the NAS., almost 24 hours.  The Mac Air overheated and kept freezing up until I removed the Roon software.  I was also unimpressed sonically, with a distinct flattening of the soundstage.
  I know bubkes about IT, but it appeared that the Roon software, which must be extensive, overwhelmed the Computer.  I am guessing that I am not the only person that has had this issue and that Roon has realized that their product may perform better on a dedicated Linux Computer optimized to run their product.  I am also guessing that they just don’t want to come out and say this, because they don’t want to discourage people from buying the software.
  I do find it annoying that the Audio Reviewers, including J.A., choose not to even pose the ?why? question in their reviews.  When it comes to collusion, the Audiophile mags and the manufacturers could show Trump and the Russians a thing or two...
 At any  rate, I am wondering if the sonic issues that I and others have noted with Roon are improved with the Nucleus

I have Roon as well. The end point is a Sonic Transporter and I access the library from an iPad mini. I can say that Roon does not catalog my library to my liking and doesn't seem to recognize my compilation CDs. Not sure if it's a set up issue or something else but I got tired of figuring it out. All the extra content, tags, and feature are kind of useless to me, but i can see why others might like the. I don't think Lightning DS is the be all end all, but it catalogs my library the way I like, is easy to use, and they seem to have gotten past quality and support issues.

In comparison, I can't say one sounds better than the other, and I'm not even going to get into that discussion since digital is not that important to me. As for Roon, I can say it does take a bit to create the library, but I haven't experienced what you have. Then again my library is about 25% the size of yours. I've been pretty happy with Synology, Minim Server, and Lightning DS so I guess I'll leave well enough alone.