You got a button 'send to S1' in Notion, that sends the dáta of your current project to S1 and also creates all neccessary tracks if told so. You of course don't get the expression maps in S1, so you have to change everything or don't use expression maps in Notion.
For syncing you always have to press one of the sync buttons in each program (both has to be running).
I in the end used Notion as the only way to get MusicXML to S1, I really don't like Notion or that pseudo-synchronizing (make that export and import so I don't need to have both programs running the samé time or do real synchronization of the two apps). But Notion (the Windows version) still has way better handwriting recognition than StaffPad, although Notion is practically abondoned, Presonus only added features to interface with S1 the last years.