I guess it is quite apparent that I am having my days with the MAS system.  So far, I have not seen anything that NAV can not do out of the box, until I got to the return orders.  ( Mind you, I am not, and do not claim to be an expert on MAS )

In the return orders, apparently you are able to select multiple documents in MAS to apply to when you post the credit to the customer.  This is not possible in NAV standard.  We have however bridged this gap with a few lines of code, leveraging the power of NAV.