Hi Colin - The Garmin Edge 25 will only accept FIT files and unfortunately we don't have a download option in this format at present (it is on our feature requests list so you can vote for it there - number 5). In the meantime you can download your route as a TCX file and use one of the various file convertors that exist to convert it to FIT format - this is one option. You then need to copy the FIT file to the GARMIN/NEWFILES folder on your device.
Hope that helps.
How do I download to a garmin edge 25?