make it easy for other 3rd party payroll companies to import their GL report to update Xero
You have a short list of payroll companies who can already interface with Xero accounting software, but I cannot find the format a general ledger needs to be in, in order to update the GL in Xero.
It needs to be easier to become one of those payroll companies, or you need to provide an import function and provide an import spec sheet.
Xero provides an API which is free for developers to interface to, and our recommended way of connecting applications.
We even have a guide on how payroll applications can integrate with Xero: http://developer.xero.com/documentation/api-guides/how-to-integrate-my-payroll-system-with-xero/ and we are more than happy to promote applications that do: http://developer.xero.com/partner/.