You have a great machine to FMQ! I have the 7700 Janome, but have quilted with ladies who use the 6600 and they do beautiful work. So, I do think the issue is with threads and needles. Machines can be cranky about that! I have found that it is extra nice to find a thread you can use in the top and bobbin, so there are no issues with little peeks of the thread showing on the wrong side. I love 50wt thread for fine stitches, but heavier wt. is better if you like to really see the thread work and it is more durable for wash and wear quilts. Don't give up, you have a machine that really purrs!