It is possible to select parameters from the children of a group and "export" them as parameters for the group itself. For example, create a group and add a Gain bidule inside it. Select Grouping: Parameters from the contextual menu. Select the amplitude item in the tree to the left and click "Add". Select the "Amplitude" parameter that just appeared in the list at right, click "Rename", and enter a new name for this exported parametes (for example "Final Amplitude"). Click "OK" to close the rename dialog and click "OK" once again to close the "Exported Group Parameters" dialog.

Now, if you double click on the the group in the patchbay you will see a window allowing you to edit the parameter you just exported. Setting its value will automatically set the value of the "Amplitude" parameter of the "Gain" bidule inside the group.

Exported parameters can also be linked in the Parameter window and controlled from MIDI.