I have one of these HP Microservers and it works flawlessly, uses very little power and because it’s a server I can do much more with it. You could put this on it and then you could also put this on it so you can access your tunes (or documents, etc) on your smartphone of choice (except windows mobile 6.x, but that’s archaic junk anyway)
It’s a bit of a learning curve if you don’t do anything like this normally, but if you can read and have a little patience then you’ll be up and running in a weekend at the very most and have an extremely capable server.
SONOS is great by the way.
You’ll need a few hard disks, may I suggest the Western Digital Green drives, they’re nice and low power, you’ll need to mirror them (easily configurable in freenas) so that should one disk go down you have the other. I’d also suggest sticking in two other drives and then you can store any work documents or whatever on that (and repeat the mirroring process) so you have access to your music and work docs wherever.
As you use Freenas with your server, you could then buy some storage somewhere and have your entire music collection available in the cloud, this gives you complete failover so should your server be stolen/faulty/whatever you don’t loose the many hours you spent either ripping your cd collection (again pretty much automated using linux) or downloaded.
Best of luck,
JT