This is from the CTO of Roon Labs. Note the end of his post where he says:
The above is pretty basic stuff, mostly focused on branding, hardware differences that must be accounted for, and delivering a polished product. The implication above is that there is some extra secret sauce for sound quality in the Nucleus’s RoonOS build, but not in the other builds…and that’s not true. If things sound different, it’s probably because of some other difference.