Okay, well then, if I were you (and again, this is just me), I would assign tblHourEnter as the record source for frmStaffReport then you can bind the Week_Ending information to the start date box and you can still assign the Staff ID to the Staff field, all while retaining your lookup function
Within this form (frmStaffReport), I'm not sure how you intend to display the "Staff" box. When I applied the record source, it retains the settings you previously assigned to it in the table, which is the 3-column setting for ID, FirstName, LastName. As I don't work with the multi-column option very often, I'm don't know there is a way to write the code so that it looks only at the ID during the openform command. So, I can only provide one of two options here:
#1 - You change the column count of cmbStaff to a one column field and only display the ID #. In that case, your VBA would read:
DoCmd.OpenForm "frmStaffReport", , , "[cmbStaff]= " & Me!Staff_ID
#2 - if you need to see the 3 columns displayed, instead of limiting your column count in cmbStaff, add another text box onto your form with the record source being the 1-column Staff ID. You can set the visibility set to No if you don't want it displayed. When I did that, the control was auto-assigned a Name of Staff_ID and the VBA was:
DoCmd.OpenForm "frmStaffReport", , , "[Staff_ID]= " & Me!Staff_ID