Hi Mick -- Editing of the metadata of music you've ripped to your Store with the UnitiServe must be edited with n-Serve (iOS or OS X) (or the Naim Desktop Client for Windows). If you try to edit with third-party software, you run into a permissions problem, as the Naim Servers make the files read-only (as edits would interfere with the metadata system they use for rips).
If you can't do the edits you want within the Naim system, the next best thing to do would be to bypass it and rip the cd on a computer, edit the data as you wish, and then put the album into your Downloads directory.
I have found the Naim system sufficient for pop/rock etc., but not nearly as flexible or wide-ranging as is available with other servers (Asset, MinimServer, etc.) where more options are available.
As for Classical . . . I've yet to find the perfect solution as to whether I want to sort by composer, conductor, soloist, orchestra, etc etc. Artist view is typically my go-to screen to pick what I want to listen to, but who do I name as the artist?? No clear approach. This has been discussed many times, and we all seem to have our own work-arounds, but no one system is good for all for classical for each of us. That's not a Naim problem . . . it happens with all servers and tagging systems. But the more flexible systems give us each more options.
NB -- You may not have access to ALL of the fields your uServe supports by default. Go into the UPNP Settings menu of the server (I use n-Serve for OS X; use that or the desktop client for windows) and be sure to enable all of the "Allowable Music Views" so that on the app you use for playback (n-Serve or the Naim App) will show them all.
