YR does use .yrm and you can convert .mpr files into .yrm files. This is the easy way, it works but you can't select you starting pointd. Go Here :

http://www.ra2md.net/files/tutorials/map_in_YR.shtml

If you have a lot of time on your hands then you can make your maps fully compatible the tutorial is Here:

http://denforums.gamingincite.com/showthread.php?s=&postid=32#post32