Hi Roc,
For your JB7 backup to restore correctly to the B2, that needs to be done using the 'Restore USB C' function.
But first, before you do anything else, I reckon that you need to verify that your JB7 backup is good. To do this, I would plug the JB7 backup into a PC or Mac and then use Win Explorer or Mac Finder to closely examine the folders and files for correct structure and content.
In the JB7 USB backup device, the top folder should be 'hardfi'. Each folder in 'hardfi' should be in the format of 'ArtistName AlbumName' (without the quotes and with 3 spaces between 'ArtistName and 'AlbumName'). Then in each of the 'ArtistName AlbumName' folders, you should see the album tracks listed.
You can back up you existing B2 collection to another USB device, but use 'Export to C' function for that, not 'Backup to C'.
Both the 'Restore from C' and 'Import' functions operate in 'overwrite mode', in other words if an Artist/Album that is on the JB7 backup is found on the B2, the B2 version will be overwritten by the JB7 version.
Your proposed course of action should work OK, but be careful of the 'overwrite' mode as explained above.
I have done a 'Restore from C' using a JB7 format backup and it worked perfectly (19,000 tracks, 1400 albums, 615 artists, 200GB volume size) so the 'Restore from C' does work correctly on the B2, but the data needs to be in good condition from the start point.
Regards,
Peter.