If you have a large score in S7.5 (30 or more), I have found that some instruments get grouped together in the mixer. They sometimes aren't even related, for example my Piccolo track is linked to my Snare (b) track. When making MP3s, it makes for a challenge to get the correct level. There should be a feature to allow for groupings defined by the user and not randomly added by Sibelius with no editing capabilities.
Idea No. 683