That is a beautiful quilt. I would not cut it down the center & have it quilted as 2 separate units. You will be loosing 1/2" when you sew it back together. I like Gay's suggestion above about removing the borders & hopefully the quilt would then fit your quilter's machine. Then you could add the borders back on when it comes back from the quilter & do the border quilting on your domestic machine. If that will not work I would find a different quilter & just pay outright for it if you can afford to.
What a treasure you have in that quilt. Give it a lot of thought before you jump into something you will regret.