Hi,
You can choose only data that are available on the server of XyGrib. For local level data, like NAM, Arome, etc. the reason is also that the number of data is huge and it will use too much bandwith and server resources to manage them.
Of course if you get them from elsewhere and they are in a format that can be read with XyGrib, no problem.
For memory, the NAM data use another projection and need first to be converted to be visualise properly whith XyGrib.