I have a Brother CS6000i and really like it. However, I would go with a machine that is manufactured by the maker of your embroidery machine because their measurements are going to be identical, or closer to just a stand alone sewing machine. I learned the hard way many years ago to NOT use more than one machine when sewing blocks. The reason is that not all machines are equal, and even though you think you have a 1/4" seam, it might be just off enough to make it impossible to get the blocks sewn together without them being a bit wonky.
As to the CS6000i and not being able to quilt on it... Yeah, the area from needle to machine head is only about 6.5", but you can quilt in there if you want to. I use a Flynn frame on this machine, and can get the frame really loaded with quilted fabric in that tiny area. I also use the plain old, use the hands to stretch lightly and move the quilt.