My Janome 4800 would only take synthetic threads for FMQ. I successfully used Janome or Robison Anton embroidery threads (recommended to me by customer services at Janome UK). I wanted to use King Tut, but it always jammed in the top of the machine. I bought a Janome 7700 at the beginning of this year, and am still getting to know it. So far I've used Superior Rainbows and So Fine very successfully. I've just done a project for the Leah Day Quilt Along using Bottom Line top and bottom, because it was the only thread I had in the colour I wanted to use. At first it shredded and broke a few times, but that stopped when I used a Schmetz top stitch needle and sewed a bit more slowly. I was very pleased with the results. I've not yet tried King Tut, apart from when I was test-driving the dealer's 7700 - it worked then, so I'm really hoping it'll be OK in mine.