I learned and carried out all my FMQ on my 6600 before I had the 8900. All machines, even the same models, differ and it's a case of trial and error to find out what works for you and your machine. Sounds as if your tension is too high. I had my 6600 on 2 or 3 tension, had my speed on middle setting. You will also find that the stitch Mode 2, number 11, works better than the utility stitch.
Used a topstitch 80/12 and successfully used King Tut, Masterpiece, Mettler Silk Finish, Isacord, Gutermann, YLI. Finer threads such as YLI Soft Touch or silk I could fmq with a TS 70/10. I used the metal fmq foot which comes with open and closed toe. An important item - do you have the "blue dot" bobbin in the machine - the tension is suited to fmq - and I also used the little plastic bobbin washers.
I think you could be manoeuvring slightly too sharp and too fast and could be why the thread is snapping. Slow down a little and move the fabric smoothly. I found the machine on fast speed also gave snapped threads, and that it was better to have the speed control on middle but use my foot to control the speed.
I did countless practice pieces before I was proficient though, it takes a while to find out what works for you and your machine. I hope this helps some.