70W is the maximum power that can be used continuously without damaging them, not the power needed for them to work. Just about any modern receiver should work fine. You can get one for less than $250.
The usual connection is (player) --> (receiver) --> (speakers)
The "player" can be a disc player (CD, DVD or Blu-ray), a networked media player or a computer.
Most modern receivers include the ability to stream networked audio sources.
You'll need to buy some speaker cabling, of course. Don't pay more than about $0.30 per foot.
I hope these comments help a little.