Sometimes more is not better -or- Ethernet Overkill

More than one person has told me Cat8 can cause noise and ground issues. I had issues with my DAC and Streamer.  Not always locking onto the signal with hi rez sources     Removed Cat8 , put 5e in and no problems 

No issues whatsoever with LinkUp Cat 8 cable in my system…running a 50FT from Xfinity Gigabit speed router to an audiophile switch. 

FWIW, I’ve tried FMC and didn’t care for the thinner “glassy” sonic signature that was the result of introducing the converters. Plus all additional clutter with FMCs and their power supplies added to my decision to send it back.
As to the CAT8 vs CAT6, I’ve tried this CAT8 from Amazon and it sounds just fine - no glare or graininess.

And I do agree, less is more has been my experience when it comes to ethernet. I use Network Acoustics Eno Streaming System (passive filter and ethernet cable) and it is excellent. 

CAT 8  is backwards compatible. In my system fiber is the bee's knees. Just goes to show YMMV and all things are not equal. I have fiber and CAT 8 from the On Q box through our entire home. Best streaming ever, now I also have a awesome digital system also. No fancy switches other than fiber. 

Get good cables, blue jeans are on the lower end of cables. Better cables will make a difference and depending on your system, the difference can be good or bad.

Dont dorget the additional power supplies you introduce with all your back and forth conversions.  They can be noisy and introduce grunge via the AC.

No issues here either with CAT 8 from Amazon (Zosion).

I have the ability to use either fiber and converters or CAT 8 over 45 feet from my router to my system. Whichever I use goes into dual Bonn switches then the NA muon system into my server. The sonic difference between using the fiber and CAT 8 to deliver the signal into the Bonn switch is subtle or indistinguishable, to the point of being imagined. I do use LPS on everything - modem, router, all switches, and the converters.

Interestingly, Rich Truss of Network Acoustics commented about the use of fiber media converters in this thread:

We’ve found optical converters actually generate considerable noise in their conversion from photons to electrons, plus the extra noise injected from their PSU’s

It sounds like it’s the answer, but it doesn’t sound so good - think listening to music from source (Streamer, CD Transport) to DAC via an optical Toslink connection versus a good RCA or AES electrical connection.

My experiences in my system have not shown what I would consider easily identifiable or repeatable sonic differences between this digital wiring stuff including Ethernet cables, fiber vs. Ethernet, switches, or even the Denafrips Hermes DDC I have used.  This stuff has been largely indistinguishable to the point of being imagined.  Based on my experiences, I suspect differences in this stuff that are actually heard (and not imagined) are likely a result of the quality of the digital implementation/termination into the specific streamer/server being used.

@erik_squires Good point on the power supplies. I have a LPS on the streamer and the far end FMC. No guarantee that the LPS is not creating noise as well, but is probably better than the supplied SMPS's.

I have concluded, unscientifically, that the issue is the Cat 8 shield connecting the devices on both ends via the metal jacketed plug, and introducing noise that messes with my router, FMC's and ultimately my streamer. I don't think there is anything wrong with these cables, they are functioning as designed, but the connected equipment is not able to deal with it. 

@rbstehno That said, maybe I will pursue some finer Cat 6 cables if they exist.

Keeping the fiber, as it is a great upgrade, just swapping out to Cat 6. If you have a little grunge on your upper end, I think it is worth a try and see if this cleans it up.

OP:

Interesting, then maybe what you need is one of these:

https://amzn.to/3q1BLHz

I do use them, both for noise but also lightning protection.  I have about 50' of Ethernet between my router and my entire HT stack, so lightning could take out quite a bit.  It's not a "surge" protector but recently I've been reading case studies on surges inside a home and isolation is preferred to surge protection once inside.

@erik_squires Good suggestion, I will look into it.

@mitch2 I'm surprised you found no improvement with the Hermes.  When I installed an Iris to use the i2S connection to my DAC the improvement was significant and immediately noticeable, and the Hermes should be even better.  What connection/cable did you use out of the Hermes and what DAC are you using?  Just curious given my very different experience.

I also use the Cat8 cables from Amazon without any problems. Using them from the modem to the router and from the router to a couple of TP boxes and then from the TP boxes to my streamer and integrated amp.

@soix - Streamer/server is the Mojo Audio DejaVu similar to this one, except mine has the JCAT NET Card XE.  The DAC is a Mojo Audio Mystique X.  I also still have Mojo's Mystique Pro DAC which, IMO, is in the same ballpark as the X, while offering a different presentation.  I was using Network Acoustic's USB cable into the Hermes and Triode Wire Labs' AES/EBU cable from the Hermes into the DAC.  Denafrips suggested I try a BNC connection and although I have not done that yet, I will try it before I decide to sell the Hermes.