[AccessD] Filtering a sub-subform

I'm having difficulty filtering a sub-subform in A2K.

The main form has subform1 which contains subform2.
A combobox on subform2 filters the records, which works when the form is
opened as a main form.
Subform1 is filtered using a listbox on subform1 and is not linked to
the main form.
Subform2 is linked to subform1.

I need to filter the records in subform2 with the combobox and still be
able to edit and add records.

How is this done?

Jim