Does it break when you sew normally? Maybe try going slower - I set the speed at about 50% for FMQ.
I'm lucky, I guess...I can FMQ on my 6600 and all I have to change is the speed and the foot. I don't change tension, no special bobbin case...I don't even drop the feed dogs anymore. It just...works. (I still kind of suck at making it go where I want it to go, but that's a lack of practice on my part; can't blame the machine for that!)
I use Aurfil or Precensia thread - both are very fine and Precensia is pretty tough. Maybe try a thinner thread?
I used to get a lot of looping on the back before I slowed the machine down, which seems counter-intuitive since usually looping is caused by moving the fabric faster than the needle. I think having the needle move at a slower rate makes me more relaxed and careful overall.