Go into the Sib user's folder (/Users/yourusername/Library/Application Support/Avid/Sibelius) and delete the "Playback Configurations" directory. Sibelius will generate a new one upon launch/restart. Create a new Configuration, see how it goes.
If that takes care of the crashing, rebuild the rest of your configurations.
I have one more idea if the above doesn't work, but try it first and let me know.
If that takes care of the crashing, rebuild the rest of your configurations.
I have one more idea if the above doesn't work, but try it first and let me know.