Will you have a Windows PC in each room?
How many rooms, and do you have the PCs already?
What kind of speakers will you have in each room, and do you have them already?
Will some of these rooms be audio only, without exception?
I have three HTPCs in different rooms with 7.1+ systems. For other rooms, where absolute sound quality is less important (e.g. Kitchen), I just bought one of these and paired with some computer speakers or Apple iPod Hifi:
http://www.amazon.ca/D-Link-Wi-Fi-Audio-Extender-DCH-M225/dp/B00KGGHYWK/ref=sr_1_1?ie=UTF8&qid=1421352533&sr=8-1&keywords=dlink+dlna+airplayI am blown away at how easily this works. The sound quality is acceptable for the rooms it's going into. The setup is easy, and "it just works". It's on all the time, extending my wireless range, and is visible through JRemote and in MC as a DLNA zone. I can link it (with a small sync discrepancy) with other zones, or play something else in that zone. I will be buying more of these and will certainly recommend them. Compared to buying or building an MC PC for $250+, you can get one of these gadgets and a decent pair of active speakers. I have no idea what the DAC is like on this thing, but for under $50 it's amazing for the type of zone I will be using it for.
Even if it's not for you, your idea of having an MC PC in each room will work perfectly too, and will even allow you to watch video as well, as well as choosing the customised path for digital to analog conversion, amplification etc. as you see fit, of course.
What you will need to do is to designate one of the PCs as the server, and ideally it will have the stored media or access to it on a network. The other PCs should be set up as clients, and ideally have the same path to the media files. EG:
If on the server the audio files are stored on a shared drive called O:\Audio\, then that drive should also be mapped to appear as O:\ on the client PCs too. That will allow each of the PCs to play back the audio as if it were doing it locally, rather than "streaming" from the server, which would act as an intermediary and use up some extra resources on the server.