I have read the manual quite few time & know the specification of NA7004 very well, it have a DAC with signal handle capabilities of up to 24/192KHz (except USB input) sample rate. As per manual specification it can play Flac files up to 24/96KHz range as DLNA Network streamer or from USB stick. But believe me (or you can confirm with other owners) it can play 24/192 KHz files very well both from Network Server and USB stick. How it is possible? I have no idea, you have to ask the company, why should I bother when I am enjoying the bonus. Might be the regular firmware upgrade support (until NA8005 came to market) had done that magic, it is just my guess.
Now this first experiment was done few months ago-
You might know I had two DAC; Schiit Gungnir & Audio-Gd FUN. Between them Gungnir had support of 24/192 KHz files but FUN had 24/96 KHz.
As I have USB stick with only 32GB space so I installed DLNA compatible Serviio (hope you know the name) as media server on my PC to stream all the vast music collection saved on the pc. I made two separate folders, one for 192 KHz and another for 96 KHz Flac files.
NA7004 was connected through digital coax to my DAC. Now rest of the process was very simple. Played some 192 KHz files from Network server (Serviio) and form USB stick both through Gungnir & FUN (switching them). With Gungnir I was getting the audio, but with FUN there was no audio (because FUN have limitation of 96 KHz).
As usual there was no problem playing 96 KHz files by both DAC from Network server and as well as from local (USB stick) source.
Conclusion:- If that DLNA server (Serviio) would had done the down sampling of 192 KHz files then definitely there would be audio signal from FUN.
So that DLNA server (at least SERVIIO) did not altered the resolution of the files.
But it was not direct proof as the NA7004 do not display the file sample rate when playing it from local drive or network server (show only tag information). But if you use NA7004 as a DAC through it's Digital inputs (COAX & Optical) it shows the sample rate of the source file.
2nd Experiment (very recently) :-
First I want to write about 'Bubble UPnP' which I installed on my Xperia & Canvas4 to use the mobile as server. It's an amazing server apps which quite easily detects all running dlna server on a network including own (as a local server) and at the same time it will trace out all the dlna streamer on that network including own (as a local streamer). So 'Bubble UPnP' can be used as junction control point to feed files between various servers and streamers. I used to use it (when the PC is off) for playing files of the mobile through NA7004 or as a local streamer (playing files of my PC using Serviio or from local storage using Mobile speaker or headphones)
Recently I found that, DLNA component has been released for Foobar 2000 (just on November 2013). I have been using Foobar for a long time and always had a wish to use it as a DLNA server. So installed that component and the Foobar server started immediately. Now I had two server running on the pc, Serviio & Foobar. Began to access both from 'Bubble UPnP' for local streaming. During streaming, 'Bubble UPnP' display the sample rate of the source file (after recent update I noticed it) on the play interface (on mobile).
So now guess what it was displaying! Bingo! It displayed the same sample rate as the source. During the experiment I disabled all the audio transcoding option of all the related server apps.
Now the Foobar DLNA (or UPnP) service have many customize options for transcoding and down sampling as per your requirement. When I had selected to down sample files to 48 KHz or 44.1 KHz on 'Foobar DLNA', then the 'Bubble UPnP app' on my Mobile also displayed the sample rate accordingly.
Conclusion:- It is a bold proof that DLNA does not alter the sample rate unless you opted for that.