even if the topic is ancient: it’s easy with a few speaker cables and a proper receiver in any room. current receivers can be controlled with any decent tablet (e.g. Apple Airplay). via the "zones" of the receiver, you can decide which input signal (e.g. TV, Sky, radio, etc.) should be played on which zone (speaker/room). if you also install HDMI cables in the walls, you basically have everything you need. :)
cost: 100m roll of speaker cable 4mm² in real copper = 120€ hdmi cable: 1-2€/m length
receiver that can do this properly: e.g. Denon 4100 or the successor Denon 4200
