For what it's worth, I do about 90% of my listening from a Sonos Zone Player. My system is simple. I have the Sonos plugged into my XDA-1 DAC, which is plugged into my preamp. I have a Netgear router that has a USB port on it. I think I paid $60 for it. I plugged a Western Digital 750gb portable drive into the USB port on the router. I got the drive on sale for $50.
I setup my iTunes so that the portable drive is the Library directory and my Sonos is setup to read music from the portable drive. Now, I just rip in iTunes and it goes straight to the portable drive. Ripping is a little slow (via wireless), taking about twice as long as it does when ripping to the internal drive, but it streams more than fast enough for music and video. My setup isn't actually a NAS, but it's been operating fine for the last couple of months.
I did, however, just order a Synology DS111 because it is a "real" NAS because I want to toy around with a Squeezebox for HD files. I'm still going to stick with the Sonos for most of my music. The system is bullet proof. I had it up and running within fifteen minute of getting it home and it's been running ever since, without a hiccup. Now, when I have a party, I just set the volume o n my preamp to about 50% and put the volume control on the Sonos to variable and me, my wife and my son all have remotes that will adjust the volume and the music.