Congratulations! I, too, have the 6600 - for 4 years now. I love it so much that I even lug it to workshops, all 40 pounds of it & I had back surgery! I tried to use my MC3000, but the new features on the 6600 just forced me to lug! My fav feature is the auto thread cutter!
Now go shopping for cones of thread at Connecting Threads. $9.99 for 5000 yards in all the neutral shades. While you're there, wander over to Batik Paradise and pick up some for only $5.96 a yard. I got some (only 4 - 1/2 yd pieces at first) to see what the quality is like - can't wait to order more.
Gosh, I sound like a commercial! Happy stitching! I know you'll love it!