Hi Zaxon,
i wanted to do the same thing as you and encountered the same problem.
I think i found a solution for it:
In the "media libary" there's also a section named "CD Media". Here you can rename the CD's. This the field "volume" in the MJ database.
Unfortunately you can't assign this field directly in the Tree&View Settings, only "Location" (with the HEX-string) you can choose.
The solution is to use one of the Custom fields (there a 3), rename one to "Volume" and then edit the files in the database and set their field "Volume" to the Name of your CD you assigned before in "CD Media". This is done easily by right-clicking on the CD in "CD-Media", "file properties", and write in the renamed Custom Field (Volume) the name of your CD, then save.
There will be errors, that it can't be stored on the CD..but it's stored in the database.
I hope this helps you organising your Mp3-CD's.
Carsten