The ones you have access to from below, if they are carpeted you can pound a long trim nail threw the carpeted floor about 2" from the wall in the location you want your box. Go to the basement and find your nail and measure over about 4" and drill up. This should put you in the wall cavity. Use a cut in box or they make a low voltage cut on ring, it's a box with no back on it. Don't forget to pull the nail out. If the floors are not carpeted you will need to find some other way to measure and drill up or use the drill bit mentioned by previous poster. I have one and use it a lot. Just cut the hole for your box and stick the drill bit in and down to the sill plate of the wall and start drilling. Go downstairs and find the drill bit and they have a hole on the end of the bit you can attach the wire to and pull the wire up with the drill bit.
As far as the floors that you don't have access from below, how are the cables run now?