They typical way that an ethernet DAC work is that they appear as a digital media renderer (DMR) on a DLNA (digital living network alliance) network. You would run a DMS (digital media server) JRiver is one example or a NAS with a player. Synology has its "Music Station". There are various players out there, and I know a number of audiophiles with the CH Precision C1 have debated endlessly that different players sound different.
If you're after What's Best, there are a huge number of variables that seemingly cannot make a difference but does.
As an example, in HiFi Critic, they found that different brands of NAS and SSD can sound different.
http://www.enjoythemusic.com/hificritic/vol5_no3/listening_to_storage.htm
Unfortunately, I think that "brand" is too gross a definition. I found, for example, that two different models of Kingston SSD sound different. I have not found a specification or measurement that can reliably give me a way to figure if a particular SSD would sound better or worse. Although, I do find in general that MLCs do sound better than SLCs. I haven't yet started exploring TLCs or serial NANDs.
That's why those friends of mine will probably never come to a conclusion. They all use the same DAC, but all they see is the interface (the player). The underlying infrastructure - the NAS, the SSDs inside the NAS, even the router used (wired or WiFi) are different. Since they only see the interface, many audiophiles assign the sonic difference to the user interface (the player). I shocked more than one audiophile when I took out my cellphone and "threw" a 24/192 file at their DAC.