It sounds like the Rino 655t will load GPX files if you place them in the Garmin\GPX folder. For example, if you want waypoints for the grand canyon you can click on the gpx link here: http://www.rivermaps.net/RiverMaps%2...%20Edition.gpx
But you'll likely get a bunch of text. Right click on the text and look for save page as, or something similar. Next be sure and save the file with a .gpx extension and under save as type select all files. (If you don't it will try and save it as a text file, i.e canyongps.gpx.txt, which won't work, you just need canyon.gpx).
Once you have saved this file, upload it to your GPS and put it in the Garmin\GPX folder. I think you can access this file like you would a route or a waypoint, but I'm not sure. I also found this: How to Load a GPX to a Garmin | eHow.com
Finally, it sounds like you might be able to open a gpx file using basemaps and use this software to send the data to the GPS.