I scanned the prior responses but don't think I saw this - forgive me all if it was there.
I don't believe the Janome 6600 has a free arm, which for me was a deal breaker since I do some garment sewing. As a new quilter, you might find the 9" harp confining. I quilted a large lap quilt on my Horizon 7700 and found it difficult but it was the first I'd ever done. Of course, it probably gets easier with experience. I like the Accufeed which both have.
One thing to consider is buying a vintage heavy duty machine for sewing layers of denim, assuming you would use basic stitches. You could probably find one very reasonably which would allow more of a budget for a new machine.
JMHO.
Good luck,
Cathy