I am not able download and check your workbook due to our network setting, but I would like to mention a couple of things :
1. If you are using data from the same data source in all the sheets of both the dashboards, then you can do the following - On the quick filter select Apply to Worksheets and then select "All Using This Data Source" in Tableau 8.0 (in 7.0 you can turn the filter into a Global filter).
2. If the data is coming from different sources, then you would have to create a parameter and use the parameter in the Filter (using the "Condition" tab in the Filter options.
You could try one of the above options to apply filters on different dashboards. I would not be able to comment further as I am not able to view the workbook.
Hope this helps.