Hi @Mark_Sealey - Late again I must stop this sleeping habit 
We are obviously on different time scales I am South Africa GMT+1
Box sets can be a mixed blessing . The rule of thumb with Big Boxes is leave them alone.
Take for example Alfred Brendel the Complete Philips Recordings . In most cases the individual CD’s we “Released” as you see them in the set. BUT not all. Some have additional tracks added to the “original CD” take for example the Brahms Piano Concerto No.1 , it has The Ballades added to the original layout.
This is common with compilations especially where the original release was an LP and restricted to maybe 45-50 mins, so they pack the CD to 70-75 mins and now Roon cannot ID it as it was never released as such. There are many examples.
So splitting a Box into CD’s won’t normally work , there are of course exceptions as ever.
To give yourself (and Roon) the best shot just set each CD Folder to CD01, CD02 etc and import the Box as is . Chances are Roon will ID it
The drawback is the “Hyperlinks from Hell” effect of big Boxes where you can’t find anything
Roon is not good with Big Boxes !!! You have to navigate in other ways eg via the Composition View
As an aside , if you add anything after the CD01 eg CD01 - Brendel Plays Bach , then Roon will see that as an album , so CD59 - Some Music Name will be treated as a solo album , Roon will try to ID and likely fail.
“words of wisdom” from some one who has got the T Shirt 