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

Oh, a second answer - to your very last question: "how can you tell".
Well, given "one equation (or test) to one unknown" - you need to compare lower to higher jitter.  Otherwise, you are hearing a system. Experience and training may tell you that sound X is related to cause Y, but that's tenuous.

Jitter is often blamed for the digital sound - the hard to define harsh un-naturalness that we've all heard.  I will say that I have been able to compare a CD on a modest transport to the same CD, ripped ALAC, and played back through a MacBook Pro, bitperfect, and a well-thought-of but modestly priced USB--> SPDIF converter. All this thing can do (good anyway) is reduce jitter. The sound was less digital (ok, whatever that means) and more transparent.  While levels were identical (duh) it sounded more dynamic, and more effortlessly so. There was more space between sounds. But it was very clear to all who heard it. It was also very clear when i got a bad feed into it switching back and forth, so that was a bit of a sanity test (sounded like crap, some USB weirdness).

Now this was not a super high end solution either, so there's more to be had. DAC was my "once upon a time it was a MSB Gold Full Nelson" Frankenstein test bed. Also the trusty old Theta that I've had for two decades.

@kumakahn.   But, do I have to have the Cambridge or some other device to just play the digital music from the NAS to start?

Once you store files on your NAS, you can play them using JRiver, iTunes, Logitech Media Server, and if your NAS is powerful enough to run Roon core, you can use Roon.  I'm sure there are other "front-ends" that you can use.

I'm going to PM you.

Of the different software out there to use what do you think is the best? Jriver? Roon? Something else?

“Best” depends on your equipment, wants, and needs.

• For my setup, LMS was best for my whole house stereo needs because I had a mix of Squeezebox and AirPlay end points.  
• I switched to Roon because of its DSP and music management capabilities, and I now have Roon ready and Chromecast end points.  
• I tried Jriver, but didn’t like the interface or complexity so I didn’t spend much time using it and I didn’t want to use a computer to run it.
• I believe HQPlayer is another option, but I have no experience with it.

With my setup, Roon is best. Roon is also the most expensive to setup and use.  You will need a fairly powerful computer/device or NAS to run Core, not to mention the annual fee or lifetime membership .  I decided on a lifetime membership.

LMS is probably the most flexible and is free, and works with about every thing.  LMS can be a little tricky to setup, but it works great.

@itsjustme.  Regarding jitter, I found this article on Audio Myths on the PS Audio site quite interesting:  https://www.psaudio.com/article/audio-myths/

Digital audio has a unique type of timing deviation called jitter, but with all modern sound cards jitter is so much softer than the music that you’ll never hear it.

My takeaway from the article is, while jitter exists in all digital music and can be measured, with modern DACs jitter is irrelevant.  I've read other articles that have reached that same conclusion, as have my ears when listening to my system.