I have a Janome MC 6700, and it can be a real thread snob. I was having a terrible time with FMQ until one of the Janome reps showed me how to reset the bobbin tension, which was a no-no for him. Apparently we dumb quilters are only supposed to rely on the top tension, but I've been sewing long enough to know that there is a bobbin tension as well, and I nagged him into it. Once he showed me where it was, voila! Would you believe it looks and is adjusted just like the one in the machine I had 30 years ago? A tiny screw right in the front of the bobbin case. Don't adjust it more than a quarter turn at any one time. Breaking thread means your bobbin tension is too tight, and in the case of machines that do both embroidery and sewing, they set those bobbins extra tight, for the embroidery, which is no wonder it's too tight for quilting. On mine, I just lift up the top plate, and I can see the screw right in front of me. I don't even have to take the bobbin case out.
Having said that, my Janome is still a thread snob. The rep told me my machine would do better with the same thread on top and in the bobbin too, and I've found that to be true. For quilting, since I still like a cotton thread but a strong one, I like "King Tut" put out by Superior Threads. Lots of colors. I've only had one thread break with it, and that's after miles of quilting. If you want different colors on the top and bottom, it also works fine by using a different colored King Tut on top and in the bobbin. As long as it's the same make of thread, it works. I haven't been able to get these pre-filled bobbins to work well.
Cheers!