Do Streamer only devices really impact sound quality?

Fatigue in the digital realm is caused by jitter, I’m really beginning to believe humans can detect extremely miniscule levels of jitter.

i agree but would add that electrical noise is also an important contributor to a perceived sense of harshness to the music - this is why filters and cleansers such as network acoustics, etherregen, optical modules and so on are able to make such patently audible improvements

@jjss49  No doubt!

One has to address both noise and jitter in order to get optimal streaming sound quality. In most cases one will have treated noise issue first since more easily addressed with more affordable devices. If still residual fatigue this very likely due to jitter. Jitter is more difficult to address, add on timing devices can't correct timing, latency issues within streamers/dacs. The jitter has already contaminated the signal, band aids don't close the wound, you could say the same about noise contamination.

So, the point is to do the least harm at each and every point of streaming chain. Per @lollipopguild every single component in chain is important and needs to be optimized. And I do observe those claiming to hear least fatiguing, most optimal streaming quality do have top tier components across entire streaming chain. I observe the best quality streaming comes from the least complex streaming setups using these top tier components, no band aids or add ons. The one exception to this is the single add on of the network devices such as Muon, in my case JCAT net XE. This seems to be critical component as routers certainly noisy and seem to be effective even for those using audiophile switches. By the way, adding audiophile switch was single worst addition to streaming setup ever experienced, YMMV.

There is interesting post here with individual going to second modem/ISP service to exclusively serve audio system. Modem direct ethernet connection to streamer and remote device such as laptop or tablet. Perhaps this setup negates need for network cleaner/filter devices?

I would definitely agree that the ethernet stage can be the most complex, and certainly seems to allow the most possible upgrades, warranted or not.

And I would certainly agree with @sns , that a decent switch can make things worse. I tried the Network Acoustics Muon between my Netgear Orbi router and my Zenith streamer and liked it a lot, until I experienced severe drop-outs (the NA guys suspected the router wasn’t very good at “auto-negotiating down to 100mb/s”). On their advice I added a bog-standard TP-Link switch with decent iFi power supply between the router and streamer. The drop-outs disappeard but it sounded awful - really brittle and bright.

I currently have an SotM ISOCAT7 and dCBL-CAT7u.

Lost my chain of thought here. I agree harshness, sense of hardness can be attributed to streaming chain and/or system. So, assuming one has rid themselves of this and still has fatigue. This is very likely fatigue due to jitter. I eliminated vast majority of harshness/hardness some years ago, eliminated minute residual over the years through streaming and system tuning. Still remained this slightest sense of fatigue,  like excess precision, a bit analytical presentation, very hard to put finger on although I began to hear it as timing issues over time. New custom streamer goes in, great attention to noise and latency issues. Revelatory is only word I can apply to what I'm hearing, much greater sense of ease, I simply relax into music, its like the music has slowed down and come into its own natural flow, far more like the top tier vinyl setups I've heard. There has been substantial reduction in noise floor as well, but the newfound sense of ease is the revelatory thing. I attribute this to great reduction in jitter vs past streamers.

New custom streamer goes in, great attention to noise and latency issues. Revelatory is only word I can apply to what I'm hearing, much greater sense of ease, I simply relax into music, its like the music has slowed down and come into its own natural flow, far more like the top tier vinyl setups I've heard. There has been substantial reduction in noise floor as well, but the newfound sense of ease is the revelatory thing.

@sns  Very well said as to the incredible improvements that can be achieved by upgrading to better components in the streaming chain.