I also have a Janome 6600. I am very happy with it. Not the biggest harp but I've done queen size quilts on it. It's not fussy about thread and works quite well. I do have to slow down when I FMQ feathers.
I've used some of the decorative stitches in my quilting. It does not have an embroidery module and that's fine with me. It isn't cheap though.
I have quilted on machines with smaller harps (small singer machine) and larger harps (brother 1500). I would never go back to a small harp if I was at all serious about enjoying quilting (especially) FMQ. I have done a king size quilt on my small singer, using a walking foot. 25 years ago. Not fun. The brother machine is a good alternative. There is a similar Juki machine. I just needed a machine that did more than just a straight stitch.