Hi JRoebke,
Welcome to the forum!
I don't think Magellan supports GPX they use their own .MGLN files. However, some of the new Roadmates come with software to help with the conversion. If you have Magellan POI File Editor you can hopefully convert files to Magellan format (.mgln file) then use the Magellan RoadMate Tools to transfer the the .mgln file from your computer to your GPS via USB cable.
Not quite as easy as with the Garmin units but give it a try.
Larry