The 6600 comes with a 1/4" foot, a 1/4" dual feed foot and a SID dual feed foot. It has a bar in the middle of the foot. I tried it but wasn't fussed, I think I do it better on my own.
Now having said all that, you should check which feet you have because last night there was someone who had been given an embroidery foot instead of a darning foot for FMQ. Check them all off against your manual.