The 9400 is a wonderful machine but you really have to learn to use it properly.
It's pretty fancy compared to the 6600. So far haven't had any major problem.
The needle threader seems to be a common problem on Janomes. Mine worked
on and off and now just doesn't work. Not enough of a problem to take it to the shop.
It can wait. I just want to warn you about the feet. If you want to do ruler work
Janome hasn't come up with the ruler foot yet. It's supposed to come
but we're still waiting. They do have the ruler foot for the 15000.
Like kalamaquilt said, test drive both machines. Check all the feet and
accessories that come with it and ask questions. Hope you'll find one
that you like.