You might just consider a traditional, receiver based 3.1 system instead. That's what I do in my bedroom, but I don't watch movies in there, so I'm not concerned about surround sound.
You're still not understanding the difference between an audio (and sometimes video) distribution system (MusicCast, AirPlay, etc.) and just some wireless speakers. MusicCast is used to do what the name implies, broadcast and play back music throughout your house. That cannot be used to...
The bottom line is, yes it can be done, but with severe limitations and a lot of potential for it not to be reliable. So, something that should make it easier actually makes it a lot more complicated, just in a different way. If someone really is intent on a wireless system, I suggest getting...
...plus, there's really no such thing as true wireless, because speakers have to be powered, typically from an A/C outlet. Batteries could theoretically be used, but would be a major pain.
Distributing music and/or video wirelessly through the house is a definite reality, but actual playback...