You have SalesAnalysis, which can mark invoices that have been paid (and the date it was paid). Woudn't it be easier to work from that file directly to AP?
You can have a GridView workspace that shows the upcoming liability and the amount that is due, as well as generate an invoice batch for importing into Payables.
Of course, you'll have to be comfortable using GridView and review the requirements of importing into either Payables or PurchaseOrders.
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Andrew Bates