Oh, so this screen shot is just a mockup?

What I would do is use the InitializeRow event. In this event, you can check e.Row.Band and make sure the row is in the root band. If so, you need to get the value from the summary on the child rows and put it into the "Main Amount" cell.

To do that, you use something like this:

e.Row.ChildBands[childBandKey].Rows.SummaryValues[summarySettingsKey].Value