1.  Remove one or as many of the stone veneer pieces as you need to remove to get your plates installed.  They'll obviously be behind the TV. There are at least 40 ways to do this, so whatever way you want to do it, is up to you.

2.  Once removed, cut through the cement board, drywall, possibly plywood too.  Now you're in the cavity that's holding the flue for the fireplace.

3. Reach your hand in the hole and find the nearest stud.  Mark that location. Now measure 16"OC for the next stud either left or right.

4. Mark where you'll drill the holes for your bracket into the studs.

5. Drill the holes directly through the stone with a masonry bit.

6. Run Timberlock screws  (length of your choosing) through the stone, cement board, drywall, possibly plywood into the stud  (Use washers around the screw head as usual)...Now your bracket is ready to go.

7. If the stone is terribly uneven to the point it's making the bracket sit wonky, you can shim it a bit with the spacers provided with the bracket...If you want to go crazy with it, you can use a dremel to cut the spacers accordingly.