MFX are one of the heaviest shafts out there, especially if you use the 50/75 grain HIT insert. On deer, don't see any reason to add tubes and deal with movement and all that. As others have said, just add point weight. With the 75 grain hit, 125 tip and feathers, you should have a total weight around 500 gpi, which is plenty for #46.
In fact, one reason I didn't get MFX other than the small diameter was the fact that it is heavy and would make a 400 arrow with 250 grain bh and 50 grain hit total over 600 grains.