Sonos is a streaming solution which takes music stored on your PC or NAS and plays it either through its own amplifier and speakers (ZP120) or an AV amplifier with a digital input (ZP90). You also have line level right and left outputs for amps without digital decoding.
The advantages of this are:
Easy to install and maintain
Can play internet radio
Can play other sources through standard line in
One controller gives full control over all zones from anywhere in the house (wireless N mesh system permitting)
Any combination of tracks can be applied across the network (playing one track everywhere allows you to walk around the house listening seamlessly - really quite cool)
Track information displayed on a dedicated controller (bit like an Ipod) so no need for TV or PC monitor to be on
System can also be fully controlled by any PC on the network and there is a free iPhone/iTouch app that will also work (via your own wireless network)
Disadvantage - you need to rip your CDs to a hard drive and tag them
have a look at
Sonos - Home for more information.