I'm trying to set up a score in Logic for multiple parts, and the horns are each in their own key signature (trumpet, saxophone, trombone) which isn't necessarily the key that the piano is recorded in. How can I get the Logic file to play back the sampled instruments with the correct notes, but have the sheet music generated display the notes as they would need to be transcribed for the live musicians? I've played around with global key signature changes and that's not helping.
You will have better luck if you post your question at the Apple Support Communities discussion forum for Logic Studio.
For instance, see this post: "How do you set up Logic Pro 9 for transposing instruments?"
I would also suggest that if you are serious about working with sheet music and arranging parts for orchestral ensembles, that you look into creating your scores in the Sibelius or Finale dedicated music notation programs. Logic's sheet music capabilities are quite limited by comparison. Sibelius and Finale both have excellent capabilities for playing back your sheet music score with virtual instrument libraries. After your score is complete, you can move to Logic for recording audio if that is required.