Not sure from your description or picture but couldn’t you add another shelf above the TV. Just drill a few small holes for the dowels on each side wall inside the enclosure above the TV. Then make a shelf and use wood or metal dowels to hold the shelf in place.
One other thought. I’m not sure of the actual space you have above the TV but it looks from the picture like the VP150 drivers might be partially covered by top front piece. Not sure but that might cause some sound quality issues if you put it inside the enclosure above the TV.
