Hello Danny,

Thank you for your post.

I have been looking into you requirements and It seems that currently what I can suggest is to use our XamMultiColumnComboEditor control in order to be able to display the information as grid in the dropdown . Currently it does not support built-in the functionality for ‘New’ and ‘Advanced’ that you are looking for. You can read more details about XamMultiColumnComboEditor from the following links:

http://www.infragistics.com/community/blogs/atanas_dyulgerov/archive/2011/11/03/xammulticolumncomboeditor.aspx

http://help.infragistics.com/doc/WPF/2015.1/CLR4.0/?page=xamMultiCCE_About.html

http://help.infragistics.com/doc/WPF/2015.1/CLR4.0/?page=xamMultiColumnComboEditor.html

http://help.infragistics.com/doc/WPF/2015.1/CLR4.0/?page=xamMultiCCE_Adding.html

http://help.infragistics.com/doc/WPF/2015.1/CLR4.0/?page=xamMultiCEE_Configuring_Item_Filtering.html

About sample application that illustrate how you can use  XamMultiColumnComboEditor as a value editor in XamDataGrid  you can take a look at the following forum thread:

http://www.infragistics.com/community/forums/t/64041.aspx

In order to be able to achieve your requirements, if you want you can get the default style of XamMultiColumnComboEditor and  re-template it,  by adding your logic for New and Advanced functionality. The default Styles are located here:

C:\Program Files (x86)\Infragistics\2015.1\WPF\DefaultStyles\XamComboEditor\generic.xaml file

Please let me know if you require any further assistance on the matter.