WElcome!! Have you tried FMQ with the feed dogs up? That seems to be a common solution. (I always FMQ with the feed dogs up and rarely have problems.) I do use a metalic needle since the scaf is larger and seems to protect the thread better. I had the 6500 and now have the 7700 and they both have a tendency to have the thread jump out of the tension disks so if I don't completely rethread I will continue to have issues until I start over, and then cleaning everything -- even one thread in the wrong place can mess things up.
There is a lot of good information in this other thread as listed by Ladyjanedoe.
http://www.quiltingboard.com/t-154486-1.htm