Re: Networked stereo - Hmm interesting
Maplin have the Alto Stealth Wireless system that could do this. It has a single transmitter and two receivers.
It's not cheap (£200), intended for PA use so the connectors are all XLR, and you'd need an amplifier downstream of the receiver on each speaker, but it would work.
You could also frig it with a stereo-to-2-mono splitter and two Bluetooth audio transmitters and receivers. Again you need an amp for each speaker, but the Bluetooth boxes are cheap and most have batteries. You could build a box to use as a speaker stand that contains one of those cheap tiny stereo amps, the Bluetooth box and a USB mains charger to power it with, or even hide it all in the enclosure of a floorstander.