SqueezeBoxes require that you run a server application (called the SqueezeBox Server) to serve your music files to the SqueezeBox player (the Touch or the Duet).
You say that you have your MP3 files on a NAS. You can run the SB Server on the NAS if it supports it, or on a PC where the MP3 files are mounted as a network drive.
Running the server on the PC means that you have to have your PC on to play music. You can have it turn on automatically via Wake On LAN, which is OK for most people.
Running the server on the NAS allows you to play music any time, assuming you keep the NAS running 24/7.
What NAS do you have? Not all NAS's support or run the SqueezeBox server very well.
If you go with a SqueezeBox be prepared to tinker quite a bit before you get things working the way you like. I am very happy with my SqueezeBox Touch, and whenever something does not work I turn to
the SqueezeBox forums.
