Funny, I just took a look at one of my m3u files this morning because I opened it on Linux and most of the songs didn't play (I saved it on Winamp). Unfortunately I had to catch my bus before I found what the problem was.
Basically an m3u file is just a text file with song names and file locations, so it should be pretty easy to do this conversion. You sound like you used something else before Musicmatch 10, did you do this with other programs?