rendu:
the_lhc:A NAS does not store audio, it stores data, when that data is being sent to another device the NAS has no idea what it's sending, it's just data, regardless of whether it's sending a Word document to a laptop or FLAC file to network streamer.
If I understand correctly, the NAS actually reads, processes and plays the data and then it sends it to the DAC or receiver. The hard drive is the one that stores the data.
No, you don't understand correctly, to do that a NAS would have to be connected to the DAC or receiver by way of and optical or coaxial digital connection or by USB. They aren't, they're Network Attached Storage, hence the name, the hard drive is just what sits inside the box, you could think of it ass a Network Attached hard drive.
The step you're missing is that there needs to be another device that pulls the files off the NAS over the network and processes them into audio which is then sent to the receiver or DAC (note that some receivers can now do this directly themselves, so this step could be internal to the receiver), which would mean something like a Squeezebox or Sonos system etc etc.
I understand that it does not play in the sound quality and I will not ask again, I believe you and my question has been answered but it is interesting that a simple cable which is only the media can make a difference and the NAS which is the player does not.
Because the NAS ISN'T the player. The NAS is just a type of storage, like a CD, in a sense.
I also wonder why there are NAS from some of popular brands such as NAIM which cost thousands.
Because they aren't NAS's in the usual sense. They are digital audio players that happen (in some cases) to have storage inside them, but they may not make that storage available over the network for anything else to access, so if you put your digital photos on there you might get upset when you can't access them.
A NAS will store any kind of data, it isn't just for audio.
There are probably also thousand of reasons but for the poor users who do not understand technologies it is a bit contradictory.
You just need to get your terminology right, unfortunately for the devices like the one you mention from NAIM and the like, nobody's really come up with a definitive name for them!