I’ve actually worked around this myself and the answer is easy!
Easy setup a new sequence that is XDCAM HD 50i.
Export from the original edit a self contained HD file, then drag that into the XDCAM HD 50i setup with the main 2 audio tracks that have everything on it. You then are free to add the other channels below! Channels in the XDCAM sequence should be dual mono and then down mix as db as your client as specified. Also be aware of how they want their audio tracks to be grouped, that setting is located on the first tap of the sequence settings.
Once your file is all set up and ready in the XD CAM sequence, export via Sony’s XD CAM export software which is free on their site. You are left with a love MXF file!
12 hours of stress may have paid off. We shall see! Thanks for the help guys!