Sorry, but this is a classic case of a room designed with no appreciation for optimizing Home Theater needs; and then stuffing it in after the fact. The proposed seating, TV, & speaker placement is all wrong.
As much as I'm not a fan of hanging the TV above the Fireplace, and using a swing down bracket, I see that as a possible solution which could get it close to a reasonable setup. Point "A" would be the LF connection point, the Center would be below (or above) the TV on the bracket, the old Center would become the new RF. Points C & D would be the surrounds.
Just my 2 cents...