Dear Quilt Crazy: I too have a Janome 6600P and am TOTALLY in love with it. It DOES NOT like Coats and Clark; neither does my Janome 350E Emb. machine.
I never pay full price for any of my thread. Please go to Google and type in sale sites for Gutterman. Next, Google Sulky, etc. This is how I get most of my thread; VERY inexpensive compared to quilt shoppes. I use rayon, some polyester and 100% cotton and varigated thread. Once you use varigated thread, you will be totally in love. I use it on my embroidery machine and you would not believe how beautiful fish, birds, etc. are. Their gills and wings just explode off of the fabric! I have a total of five Janome machines and love each and every one of them. Enjoy your machine/s. GiGi :D :D :D :D :D :D :D