Unlinked Subforms

I am using Access 2003.

I have a form with 2 combo boxes. These are to choose criteria to populate a subform.

The forms are not linked.

I want to assign a different Record source property to the subform depending on the values provided in the combo boxes. The issue I am having is locating the correct syntax for the record source property to be updated.

I have tried

Forms!frmUpdateIssueDueDate!sfrmUpdateIssueDueDate.RecordSource
Me.sfrmUpdateIssueDueDate.RecordSource
Forms!sfrmUpdateIssueDueDate.RecordSource

an a few other combinations and they are not working, any suggestions?