Do I have to use a streamer/renderer to play music from an NAS?

Just to answer a few questions not addressed to me :-)

-- Why have the server in another room?  I think to reduce physical noise (fans, etc.).  I probably will just put it in a closet in the room.  I'll also make a quiet server based on  NUC, Roon ROCK, etc.


-- Why is Ethernet superior to USB?  answer: both are asynchronous and therefore should be the same. But USB needs to be galvanically isolated to prevent noise propagation. Also, see above, network allows you to remote the whole thing and eliminate physical/mechanical noise

Otherwise there is no difference.  Either vs SPDIF is a big difference however, since SPDIF is synchronous and depends on the source clock, which you cant control.
G

Wow, what a wealth of information. I appreciate it so much.  But, honestly, I just want to listen to music that sounds great and is easily located and selected. I spent too many hours configuring networks, etc. when I had my own business. I want simple but good sounding. Much of this seems too complicated for my tastes. Is the Bluesound Vault II reliable, especially the built-in ripper?

A huge resounding YES on the Bluesound Vault 2.
Used one for two years with zero issues on streaming or cd ripping.
It is very versatile although it’s weak point, imho, is its internal dac.
For a grand its a simple powerful way to get round any tech issues, it s nearly plug and play.

@kumankahn.  But, honestly, I just want to listen to music that sounds great and is easily located and selected.

Looks like you have to main goals for your music: (1) sounds great  and (2) is easily located and selected.

(1)  Seems like a hardware choice.  Since your RC-1590 has a DAC, I'd look for a pure media server.  Take a look at the Innuos ZENmini  
http://www.innuos.com/en/catalog/go/zenmini-mk3-1tb-hdd. 

They are simple to setup and configure; are CD rippers; and come pre-loaded with Roon.  They cost more than the Bluesound Vault 2.  I use a Zenith MKII.  The SQ is outstanding.  Check out the online reviews.

For connectivity, the ZENmini has two Ethernet ports or a USB port.  In your case, you would connect your LAN cable to the ZENmini "LAN" port, and then the ZENmini "Streamer" port to you RC-1590 "Ethernet" port or the ZENmini "USB" port to you RC-1590 "USB" port.

(2) Seems like software choices.  I'd give Roon a try.  If that doesn't work, there are a lot of other choices.

"But, honestly, I just want to listen to music that sounds great and is easily located and selected."
:-)  Don't we all. Let us know when you find it.
Ok, seriously, its not that easy, but yes BlueSound is supposedly pretty good. But you still either need to co-locate it with your DAC, or you need to get something to terminate the network in another room and feed either USB or SPDIF to your DAC, and therein lies more complexity if you want good sound.  Its mostly about digital noise on the line and jitter.
G