If I understand correctly, you are looking to mount into the drywall/stud on the wall perpendicular to the stone fireplace but then rotate the speaker so that it points in the same direction as the stone wall (i.e. the stone wall is your back wall). In that case, the Axiom mounts don't stick-out enough for a full rotate.

One option would be a longer mount like these:
https://www.amazon.com/Stage-SS7914B-Mou...&dpSrc=srch
You would need a bracket to fit over the pole mount to anchor onto the QS8s

You could also go the DIY route using black pipe and fittings found in your local hardware store. You would need a floor flange to mount to a stud, an 8" pipe, a 90 degree elbow, another length of pipe to bring QS-8 flush with stone wall and another floor flange to mount the speaker onto... I've done this in the past as a DIY projector mount with a piece of wood between the floor flange and projector to properly align screw holes.