visit google for those oragami style passive reflectors, you print them out, fold them and glue on aluminum foil ... direct the energy you have into the areas you need, rather than just putting out more energy in all directions.
if you think about it, with your antenna in the basement, more than half your energy is directed into the floor of the basement and into the walls, only a small percentage radiates "up" ... if you build some reflectors, attach them to your antennas, and reflect all your radiation "up" you should see a marked improvement.