Here's how you should think of it: Instead of of the data going from a hard drive, along a SATA cable, to the motherboard and so on it's going to do that same set of steps but with a wireless transmitter and a wireless receiver in the mix. However, you're streaming data and as such it's going to arrive bit for bit exactly as it started on the other end. In that sense there is no difference between music stored locally, on a DAS, an NAS or some far-flung remote server.
The difference comes in things like responsiveness and latency. With internal storage and DAS there's almost no latency but in anything over the network there always is. Will there be enough to effect playback? Most likely not. If you are using Wireless-N and have a strong signal the worst you're ever likely to get is a one second delay when you start playing. But once the NAS has a connection and is awake and running it'll likely give you similar performance to DAS.
Remember, you're not streaming 1080p video here, Even the highest quality music won't touch the speed you can put through a good wireless-N network.
However, if you start streaming, someone is gaming, someone else is transferring some large files and someone else is watching Netflix or something you might start to notice some increased latency. If that does become a problem simply run a CAT6 cable from your router to your computer and it'll go away.
Out of curiosity, why are you going NAS? The purpose of a NAS is to allow multiple devices to access content from one centralized location at a time without having to open up one computer. If all you want to do is move your music off your computer you could spend less and get an external hard drive.
A good NAS is going to run you a few hundred fo ra cheap one where you can expand your storage for the price of a drive and case.
