I have the same machine. I also have been having trouble with the thread breaking when I do free motion machine quilting. I have had it in to be looked at several times.....After cleaning it and replacing a part, it is still breaking threads. (And it is just your average 50 or 60 weight thread, nothing fancy...) I have been told I need to adjust the tension.....
I hope that works!! I'm trying to complete a Christmas gift.