I worked out yesterday that I needed to use seperate dataSources (with Static Filter) to achieve this and ran into the issue you mention regarding drill down. Can you provide any more detail on the solution you mention above? Is there a way to keep using the pie chart as the drill down filter and get it to apply to each dataSource.
The other option I thought about was to have all the information in 1 DG (and on dataSource) and continue to use the Pie Chart as the filter (Stage) but when a filter occurs I could show/hide certain columns in the DG. would this be possible?
Are there any plans on development to extending filters to work across multiple dataSources?