I've combined 2 of your demos, the grouped data one, and the filter directive one. Filtering doesn't work in this example. Is it possible to make the filtering work with the directive? (I assume I can fall back on manually filtering the data).
You can use the Data Query process() function to apply grouping and filtering simultaneously and assign the "data" property of the resulting object to the field the ComboBox "data" input is bound to, for example: