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

One other thought if you did say go the Synology route you could run a digital cable from whatever device you have Disc Station Manager on, laptop or whatever, to the dac in your preamp. You may need a usb to coax converter unless your preamp has a usb input. You can use Audio Station on DSM for playback there are also other playback options available on DSM like Plex and Minimserver.

If you want world class sound, keep any pc/Mac/music server out of the room. Put your server in another room and get a good dac with a network card in it. 
Also, you don’t need a music server/renderer to get music off a nas. If you have a good dac with a network card, use a Mac mini running Roon from another room. Roon’s Interface and SQ is so superior to other mentioned above. IMO the next best would be auralic’s DS Lightning interface.
Any good quality 1G switch will work. I have never had a switch deliver invalid data. If you can hear a difference between switches, the routers, wall plates, Ethernet ports from each device would be called into question.
I actually had a vendor tell me that they only used a specific hard drive because they could hear a difference. When I told him I worked for Seagate that made the hard drive he was using he backed off since disk drives change constantly and the drive he was buying today might be different from what he buys tomorrow.

I've had Steve/Empirical's Interchange here for the last week or two. I haven't had a chance to critically A/B test it against my other streamer, but it's definitely sounding outstanding. Coming from Roon, the Lumin Kazoo software is just barely tolerable, but it is probably about as good as anything else I've used, and it does run on iOS as well as Mac desktop/laptop, and that's important to me. I'm also using it to try out Qobuz and have that working, streaming hi-rez files is pretty damn nifty. I like the idea that it's made by one guy with extreme attention to detail. That's how the rest of my system is configured. Anyway, I hope that's helpful. DM if you have any questions about it. 

I should add that I keep my music on an Intel NUC running Linux/Minimserver/BubbleUPNP, and I have exactly the switch/isolator/cable setup Steve describes up there ^^^. That cost a few bucks, but it sounds real nice. 

You have the basics above. I’ll just add a few comments.
First, think about the tasks - you need something to catalog and let you browse and select a file to play. Someone mentioned ROON, and i think that happens to be the pick of the streamer litter. Next, you need to get it to the room your stereo(s) is (are) in. This is any old ethernet network - not Wifi preferably (although it may work). Next you need to terminate the ethernet, convert it to either USB or SPDIF and provide that to your DAC which may be in a receiver or may be stand-alone. There are bunches of these, one by ALLO based on Raspberry Pi is excellent for the money.

Note that the digital signal DOES impact sound a lot, for good reasons, mostly 1) jitter and 2) noise, which causes 1) (jitter). Its HUGELY important. I was shocked.

Consider both what you need to get ot to play today, but also what you want for the future. I want a single server with a great interface for all my music, radio, streaming subscriptions etc. This will be ROON on a dedicated server (NUC/ROCK/custom linear supply). AS long as i can make that electrically and mechanically quiet i do plan to have that as part of my main system and drive my DAC via USB directly (well, galvanically isolated, but that’s about the noise bit).

Commercial streamers like SONOS and Bluesound simply combine some of these functions in the head-end and others int he remotes. SONOS, by the way, sounds awful in the context of true high-end. I was also shocked when i first heard that in a very good system. Switching ti CD was a relief.

I need to look up audioengr’s roll-you-r-own components to see what its about. I don’t think i’d give up ROON though.
G