I myself would go and get a Samsung S5 and have it rooted and install some T.W.R.P. Jazz that bad boy up with some Xposed framework and your good to go, as that among other things will enable you (after you then install the Xposed apk and proper xposed module) to write to the ex S.D. with up to Android 6.0.1.
This is one reason I was never enthusiastic about the S6 or S7, Corning glass? It looks nice but don't drop it! Gorilla glass is fine for me!
Feature wise, the S5 was the prototype for the S6 and S7 and it should cost you less than what you would spend to repair your S7.