Weakest digital link: DAC - Streamer - Server?

To sum up however because Cindy will be along shortly to tell everyone what's what.

Gotta love it when your reputation proceeds you ....

Let's do a thought experiment:

I make a DAC. The DAC has a SD memory card on which there is music. The DAC of course reads the music from the memory card, puts it in a buffer, and then plays it out. What impact does the SD card have on the quality of music assuming it is not broken? None. I think most would accept that. If someone does not, then an reasoned discussion is impossible.

Now let's say I have a cheap server or expensive server/streamer, and it connects to my DAC. It does it using USB or Ethernet. The DAC just like above, reads the data (perfectly), and puts it in a memory buffer?  How is this at all any different from the above? From the data side none. They both get perfect data.  One one and singular difference is noise. So now we know the difference between a SD Card, a NAS/Computer and an expensive streamer is purely noise.

Ethernet:  This is already electrically isolated. There is a transformer on each end.  That is pretty effective noise isolation. Being Ethernet, you can place your hardware a distance away if you are worried about AC noise, and/or buy one of many AC filters.  If you are still worried, there are Ethernet filters that claim to remove unnecessary frequencies from Ethernet  (keeping in mind you already have two isolation transformers).

USB: Direct electrical connection, hence high potential for ground noise. No worries, a really good USB isolator is about $300, maybe $400 with a linear supply. I hear Topping has one <$100 now. Optical isolation. No direct noise path. You have some distance limitations.

What are you missing? Nothing. You seem to understand the basics just fine.

The oft repeated saying "The chain is only as strong as its weakest link", sounds nice, but wrong. How about looking at it another way. If the chain does not break, then it does not matter if any of the links are stronger of weaker. It is good enough to do the job. But that is still wrong because it is not a mechanical chain, it a processing chain.

NAS = -40db noise, DAC-A = -80db rejection - final result = -120db

High End Server = -60db noise, DAC-B = -50db rejection - final result = -110db

Well what do know, it is not about the weakest link, it is the combination. But frankly it does not matter, you would not hear something -110db or -120db noise with music playing .... the chain is more than good enough.

TEST A: Plug / Unplug Ethernet with the volume at the max of the listening level. Do you hear any change in noise? No, then you don't have an analog noise issue.

TEST B: ... really there is no test B, because the next claim will be "well what about digital noise hurting the clock". Well if the analog noise is so low that you can't detect it or super faint, what are the odds it is impacting the super fast transition of clock signals that are at least 1V?  The noise from the internal circuitry in the DACs digital section is likely orders of magnitude higher than external sources with Ethernet or isolated USB.

Thanks Cindy, so my assumption is CORRECT, having my Audio files HOSTED on my NAS in a separate room and using a good streamer/DAC to play them will yield the EXACT same results as if I had a dedicated Audio server (Innuos, etc...) in the same room - BOTH connected via the same network/ethernet cable!

From what I can gather, the dedicated music servers just make the life easier, and make it dumb proof for folks to host their files (Innuos is super easy), but for anyone with technical background like myself, I can simply put my files on my Synology Audio folder and have exact same results with data redundancy, backup, remote access and ease of use! It's currently hosting 4K videos without a problem.

I guess my next question is, WHICH streamer/DAC, under $2K, would do the job best playing files off my NAS PLUS having Tidal/Spotify Connect?

Roon helps consolidate a library with multiple sources. You can use anything from a laptop to an expensive music server as the Roon core. Link your Tidal or Qobuz account to Roon and continue using your NAS for local files. A simple Raspberry Pi can be used as the streamer/Roon endpoint, and allows for the DAC of your choice. You can also use any of the countless streaming DAC's. Companies like Auralic have offered streaming DAC's for many years. I personally use an Okto Dac8 Stereo, which has an integrated RPi acting as a Roon endpoint. The Okto is $1500 and is a superb DAC, although difficult to purchase from high demand/low supply.

As long as all the devices are connected to the same network, it should work.

@alexb76 

People are still making claims about digital that have not been true for decades. This is just one of them. There used to be problems with jitter on TOSLINK, but then just don't use it. The rare time you may get jitter on SPDIF if poorly implemented, but then just change the cable length. Noise on SPDIF is a potential issue, so buy something with transformer isolated SPDIF. USB can present electrical system noise, so isolate it. Hard to comment on Ethernet noise. Many claims, nothing to indicate any level of testing. Theoretically possible, so if you feel the need add a filter.  Computers can have noisy power supplies, but then again, linear supplies create awful harmonics on the AC line with lots of current/power. But you can remote your hardware or buy a filter.

Agreed, items like Innuos are simple, and make sense for many audiophiles. Time is money, and most don't have the experience. A lot of the reticence of using PCs as streaming sources is not just USB, but inability to set up the system so that you got bit perfect, and Windows or OSX was not inserting sample rate conversion, limiting, etc. in the middle.

@Op

I applied this approach initially with the Node 2i and I do not notice any obvious difference between music on my PLEX Server- WD PR2100 - versus IDAL on my streamer DAC.

My server with PLEX installed is connected into my router via ethernet as is my stream/DAC.

I find I stream much more than I use my server - I can't recall the last time I bought a CD - mid 2000s. 

The upgrading from the Node 2i to Moon 280D did make a huge sonic improvement.  Lots of options at $2-3.5k price point.  Part of the reason I bought the Moon unit is they advertise they design upgradability into their equipment.  

And my stored music isn't changing format  - so really the only value I get out of new technology capabilities is with new music in high resolution format.  

Hope this is constructive.