I also have a Janome 6600 Professional machine. I have had many machines in my lifetime and this one is the greatest.
It has a long neck for machine quilting, A built in walking foot
A scissors (built in) to cut threads on the top and bottom. The best needle threader that does work, and a locking stitch to tie your sewing. Up and down needle in & out.
Before I had the 6600 I had the 9000 Janome embroidery machine which I still use. And for classes I have the Janome 760 Gem .
I love them all. I have been sewing and quilting 25 years. Good Luck in picking a machine.
Gert in MA