I just completed upgrading this widget to Mx6. The test project is working for all cases, but I'm still testing this in my own project. If this all works all create a pull-request for Andries and see if he can update this to the appstore to.
You could try and use this temporary version if you need to move forward: https://github.com/jaspervanderhoek/DataGridExtention/tree/master/test/widgets
Data grid extension was not yet updated in the mendix app store yet. Even I facing the same issue.