Hi Adam,
Thanks for the being patience. Currently it is not possible to implement GridControl or DataBoundGrid with ComboBoxBase. Another Option is to use the grid in the Popup control of ComboDropDown Control or else to use the grid in the PopupControlContainer.
Sample:
The following sample demonstrates the GridDataBoundGrid with 20,000 data’s being dropdown using PopupControlContainer
GridInDropDown.zipPlease refer to this KB article link for more details.
http://www.syncfusion.com/Support/article.aspx?id=10090
Best regards,
Madhan