Even wireless active speakers needs power to drive the build-in amps.
Opalum has a very specific solution.
The speakers are fed (24 V) by a dual wire connected to a hub.
The signal is transferred over the same wire.
You can connect the speakers parallel or daisy chain them.
The hub takes care of the connectivity.
Analog and SPDIF inputs
Wireless b/g with Airplay and DLNA.
Website: Opalum