Hello @John_Cross1 ,
Thanks for your query. I looked up this device and I was able to find the manual for the C2700 at the below link:
https://www.mcintoshlabs.com/-/media/Files/mcintoshlabs/DocumentMaster/us/c2700om01.ashx
From page 27 in the manual, I see this listed:
The C2700 USB Input is compatible with PC Computers using Microsoft®, Windows 7 (SP1), Windows
8.1 and Windows 10. It is also compatible with Apple® Macintosh® Computers using OS-10.6.8 or later.
I don’t see any mention of Linux compatibility via USB (and Nucleus runs Linux), so I would reach out to McIntosh to confirm this, but this incompatibility may very well be the issue of why it is not appearing.