Just wanted to throw this out there if streaming music is in your plans. Pandora and some others stream lower quality when played from Sonos, Squeezebox, Airplay, receiver, etc as compared to from a computer so you might want to pay attention to that. Also, very few streaming services have parental controls (no explicit music), which is important to me.
With the previous mentioned, I would really like something that I could use that would be computer based to ensure higher streaming quality. I've looked into Raspberry Pi, multiple apps, etc but didn't find anything. One option that I might try is running several WinXP or Win7 VMs using VirtualBox with Expansion Pack (direct USB access from VMs) and then sharing the apps using the utilities below. I would then use USB DACs to drive the amps. I would then need some sort of matrix audio controller to switch source between rooms and I've been looking at this (
http://www.ebay.com/itm/Autopatch-AMX-Precis-8x8-DSP-Audio-Switcher-w-RCA-/140795973521?pt=LH_DefaultDomain_0&hash=item20c8180f91), which is controllable via RS-232 for Homeseer, CQC, etc.
https://sites.google.com/site/kimknight/remoteapptool (Utility to setup Windows Remote Apps)
http://www.jumitech.com/index.php?page=tap (iOS, Android)
Now that I think of it, seems pretty complex and after buying the matrix switch and USB DACs, I wouldn't save THAT much, especially once I include the time it would take me to get it working and I hate getting that call from the wife saying XXXXX doesn't work.
Squeezebox sounds good, hope it meets your needs and you are able to get it working satisfactorily.
David