It is absolutely essential that PO-related supplier invoices be entered in DBA so that they can be matched with PO lines.  The matching process closes PO lines and adjusts the Received Not Invoiced account for any variance between receipt cost and the invoice price.  When invoices are transferred to your accounting system using the AP Voucher Transfer screen, the invoice amount is charged to your AP Voucher Transfer control account.  Any attempt to bypass or alter this process will cause severe workflow and accounting problems.