I think that there is enough space to install the fixtures, but it might be a little tight. What I would recommend doing is making a template of the wall sconces in cardboard or paper and tape them up on the wall to see if it looks too crowded. I do think that you have chosen sconces that are a good scale for the space you have available to install them. Putting them up on the wall would also give you a good idea of what the correct mounting height would be visually. If it does seem a bit crowded, is there room above your fireplace to mount the speakers horizontally above and below the television? I am usually lying down when I'm watching TV, so that way the speakers would parallel my ears.