Naim claims that the NS C222 is ‘Roon ready’.
You focus on the USB (external storage only) and the SPDIF inputs (max. 24/192 PCM and DSD64 DoP) only. The Naim also is a streamer with an Ethernet connection also and can function as a Roon endpoint. It can also do UPnP. Maybe that’s your missing link?
Roon via ETHERNET - Support - Roon Labs Community
What I see in their documentation seems correct.
Why do you think it is a ‘clever play with numbers’?. Naim is, in my experience, a thrustworthy company. If they would be ‘dishonest’ about any of this they would be keelhauled all over this forum.