You will need to do the following to import both the baseline and the update into Synchro:

1- Export the baseline from P6 to P6 XML
2- Import the baseline P6 XML to Synchro
3- Select all tasks and Baseline Selected Tasks to save a Baseline
4- Export the update schedule from P6 to P6 XML
5- In Synchro, go to Navigator>External Data, right click on the imported baseline schedule and Synchronise From to synchronise the changes from the updated P6 XML. 

Then you will be able to see baseline/update bars in different colors in Synchro.