Has anyone attached two HDD to their Nucleus or NucleusPlus? Have you had any issues with the server merging the data from both?
This is really no different than adding multiple network shares to Roon. It will handle the library fine. After all, it thinks of your music in the sense of artist/album/track not file paths. The file paths are just a technicality to enable actual playback of the file. (If the files have no metadata in them then it will try to guess at some of it based on the file path, but unless you library is full of WAVs, that’s unlikely to be an issue.)