We support Barcode scanning at the Purchase order and sale order.
If you create new a PO or SO you will see a "Scan items button" (see picture below)
That said, you need to track inventory inside Stock&Buy. We don't send products to Xero, just invoices. Will automatically send purchase and sales to Xero. So you can continue sending invoices from Xero or send them from Stock&Buy.
Would that work for you?
Let me know if you need more details.