Hello j!
I think some setting must be wrong then. Slurs just add the Sound ID +legato and thus will trigger the legato patch. So if you want to hear legato phrases, excluding slurs from playback isn't exactly what you'd want to do.
Please can you tell me which instruments don't work as they should, which Sibelius instrument you chose for them, which program you have set on the manual sound set page and which channel and sound ID appear in the Sibelius mixer for them.
If you haven't done so, please make sure that with instruments you use more than once, you will also have to reserve more than one channel on the Manual Sound Set page.
Best,
Andi
Vienna Symphonic Library