why expensive streamers

Why are people spending 1000's on streamers?

No idea, but I will be interested to learn why.

I recently had to change out my server, and found that pretty much whatever server I used had virtually no impact on the sound of my system. But when I changed out streamers, I encountered a significant impact on how things sounded.  As one example, I own Metrum's Ambre, which is a raspberry pi based streamer with its own internal linear power supply and femto clocks.  I always thought it sounded pretty good but the Sonore Signature Rendu SE optical sounds more dimensional and seems to portray a more realistically rounded tone.  The price difference is about $5,400 vs. $1,200 and to me, in my system, the price is worth the improvement in sound quality but, again, I have no idea why.

Within the context of my digital music playback system, which involves using Roon to stream Tidal and Qobuz, and to play stored music files, my hierarchy of  differences I hear is:

• Server/Roon core: almost no differences heard between servers
• Fiber optic vs. Ethernet: little to subtle sonic differences at most, but not reliably discerned
• Switches, on-line tweaks, and decrapifiers: no reliably heard differences
• Streamer/Roon endpoint: more substantial sonic differences and the ability for some streamers to significantly improve sound quality
• DDC: Little to subtle sonic differences noted, at most
• Digital cables including USB:  small differences between coax, AES/EBU, and USB, but very little to no differences between different cables of the same type 
• DAC: Each displays its own sonic flavor and can sound substantially different from each other

In summary, I have noted differences in the sound of streamers and DACs, but not  much with anything else in the digital chain.

@andy2 

So, if you connect your server to your streamer using an optical cable, and USB from the streamer to a DDC that reclocks, and then a short s/pdif or AES/EBU to the DAC, are the bases mostly covered? 

I can use either s/pdif, AES/EBU, or USB into the DAC.  I could run USB directly from the streamer into the DAC, or I can run the USB from the streamer into the DDC where the signal is reclocked and then from there to the DAC by either s/pdif or AES/EBU.  All three sound good with no discernable noise but maybe a slight sonic difference between USB and the other two.  Any technical reasons one should be better than the other?

I am curious at what point a typical digital signal is subject to being processed, changed, or influenced by noise as it travels from a streaming service via modem/router through to the DAC? How about in the case of the following digital streaming set-up:

• Into and out of a server via Ethernet,
• Into and out of a switch via Ethernet
• Into a streamer via Ethernet (or fiberoptic) and out via USB
• Into a DDC via USB and out via S/PDIF or AES/EBU
• Into a DAC via S/PDIF or USB and out via analog cables to a preamp

Obviously the DAC converts the digital signal from digital to analog but which of the other preceding steps has a significant impact on the digital signal?

I am confused about "no jitter."  When I was looking at different DDCs, I came across this review about the Singxer SU-6 model, that I ended up purchasing.  The reviewer performed measurements and at that time the SU-6 had the lowest jitter of units they had tested, but there was still jitter.

In addition, the reviewer discussed noise and said:

The second issue that a good DDC or Streamer will seek to address is electrical noise. You don’t want noise from your source causing your DAC to perform poorly. Noise can have a direct, audible effect, such as hearing GPU-whine through your headphones/speakers, or it can have indirectly-audible effects. For example, causing clocks in your dac, or other circuitry, to perform sub-optimally.
Some dacs are more immune to this, and some will even have full galvanic isolation to in theory prevent any noise getting through entirely. But many smaller dacs are much more susceptible to it.