The best way to create a multi room music is to go for Apple’s Airport Express.
Do not waste money in setting up expensive multi room music system like Sonos or Sooloos(!). Go for cheap and cheerful Apple Airport Express solution. All you need is an old PC, iTunes, and your existing music systems in different rooms. If you have an old iPod Touch, you will be laughing – it makes a great remote for this multi room system. Oh – you also need a WiFi network at home.
You can later buy an interesting application called AirFoil, if you want to transmit music to Airport express from other music apps like LastFM, RadioIo, WinAmp etc.. In this case, you can use RDP Lite (free iPhone app) to control the PC remotely, if you are too hung up on doing things remotely and impressing your friends!
And if you want audiophile quality and have some money to burn think of investing in B&W Zeppelin which pairs up with Airport Express using optical connection. Sublime!