I have both the 6600 and the 7700, have not found any difference in the machines other than the 7700 has a few more stitches and a little larger harp space. The 7700 also does not have something that the 6600 has but at the moment can not remember what it was. The 7700 has it tool boxes attached to the machine, you can remove them which is probably best to do as the tools rattle when you sew. The 7700 does have better lighting so that is a plus if like me you have poor eye sight.