Hi Warren,
Unfortunately, in order for Roon to connect over the network to the Cambridge unit, it requires either that Cambridge upgrade the firmware to be Roon Ready or that you have access to the operating system in the unit and it is running on hardware supported by Roon Bridge.
User access to the operating system is most unlikely, so asking Cambridge about their Roon Ready plans is the best course to make that happen.
In the meantime, you can use a Raspberry Pi or CuBox, load Roon Bridge onto it and have it act as a network endpoint to Roon connecting to the Cambridge by USB or Toslink (CuBox). You’ll find guides to installing Roon Bridge onto those devices in the Audio Products/Raspberry Pi section of this forum.
Sonore make a commercial version of the CuBox with all the software installed (SonicOrbitor SE) or their microRendu is the best Ethernet to USB connection I know of.