How can different CAT5/6 cables affect sound.

I think this is just the tip of the iceberg. There’s also watermarking, remastering into high resolution, compression. It then gets to our streamers where proprietary DSP takes place ingesting and processing the incoming stream. Some would endlessly tweak their network configuration and set up with filters, regenerators, switches, reclockers and other bandaids. I’m not saying streaming is inferior but it is kind of like a kitchen in a restaurant - you just don’t know what’s involved in cooking that meal you ordered.

CDs and vinyl records still sound excellent. Streaming isn’t superior. It’s just very good and very convenient. And I think it is getting better as technology evolves on both sending and receiving sides. 

@panzrwagn  These are situations for which the impact of EMI/RFI on the digital conversion process will be audible if error recovery is not instantaneous as well as potential impacts on analog output stages.

@devinplombier The following digital impacts (#1 and #3) are errors in digital-to-analog conversion, not in transferring bits for which any errors can be resolved with error checking and a buffer. A buffer doesn't help in these situations because EMI/RFI is affecting the validity of the output from the digital-to-analog conversion process.

1. Clock Instability creating Jitter

• How it happens: EMI/RFI couples into the DAC’s master clock circuit, nudging the timing of when each sample is converted.
• Effect on conversion: The DAC still outputs the correct voltage levels, but at slightly the wrong instants in time.
• Audible impact: Treble glare or “etchiness”, Flattened stereo image, Loss of spaciousness

2. Coupling into the Analog Output Stage

• How it happens: After the DAC chip outputs a small analog voltage, it’s sent through op-amps or discrete analog stages. These are high-gain, wide-bandwidth circuits — practically antennas for EMI/RFI.
• Effect on conversion: Adds a noise floor “haze”, Can cause intermodulation distortion (high-frequency interference folding down into the audible band)
• Audible impact: Graininess, Fatigue in longer listening sessions, Reduced warmth and realism

3. Reference Voltage Pollution

• How it happens: Every DAC chip uses a precise voltage reference to decide, for example, “this bit pattern equals 0.734 V.” EMI/RFI sneaking in via the power supply or ground can modulate this reference.
• Effect on conversion: The DAC’s internal scale is wobbling, so each sample isn’t output at the exact intended level.
• Audible impact: Subtle distortion, Loss of microdetail, “Gray” or veiled background instead of black silence

@calvinandhobbes So what you're saying in your examples is that cables are making no difference. Got it.

However, your hypothetical, post transport 'digital impacts' are not bounded by any quantitative values, yet they are specifically quantitative, e.g. "DAC still outputs the correct voltage levels, but at slightly the wrong instants in time" How much time are we talking about here? For example, memory chips there is a specification for variations in edge trigger (the point when they transition from a 'zero' to a 'one' - all bits should do this at the same time) that determines their upper bandwidth limitation. So be usable at 1 GHz the edge triggers must align within 1/10^9 or 1 nanosecond. The requirement for audio is ten thousand times greater, 10 microseconds or 100KHz. With modern chips and memory routinely operating in the 2-4 GHz range audio is not a very high bar for modern digital circuits. Concerns over picoseconds or nanoseconds of jitter are pointless when the requirement is ten thousands of times easier..

"Adds a noise floor “haze”, Can cause intermodulation distortion" The noise floor is a quantitative value, so any perturbations of it should be easily documentable, as should the threshold of audibility. Right now, in my office I'm listening at an average level of about 68 dBA, with peaks of 87 dBA. The noise floor is a very quiet 40dB, so the dynamic range of my system is 47dB. Adding 10, even 20dB of volume and the total dynamic range is now pushing 60-70 dB. Any argument that that these artifacts, existing 80dB, 90dB or more down, are audible are specious at best. 

Reference Voltage Pollution "The DAC’s internal scale is wobbling, so each sample isn’t output at the exact intended level.". Again, this is a quantitative value, so some examples of how much 'wobble' is occurring would be highly illustrative. 

For context, TTL gates operate on a nominal power supply voltage of 5 volts, +/- 0.25 volts. Ideally, a TTL “high” signal would be 5.00 volts exactly, and a TTL “low” signal 0.00 volts exactly. 

However, real TTL gate circuits cannot output such perfect voltage levels, and are designed to accept “high” and “low” signals deviating substantially from these ideal values. 

“Acceptable” input signal voltages range from 0 volts to 0.8 volts for a “low” logic state, and 2 volts to 5 volts for a “high” logic state. 

“Acceptable” output signal voltages (voltage levels guaranteed by the gate manufacturer over a specified range of load conditions) range from 0 volts to 0.5 volts for a “low” logic state, and 2.7 volts to 5 volts for a “high” logic state.

The devices 'wobble' has to be pretty severe - defective - for this to even be part of the conversation. 

Cables make a difference by their ability to channel stray EMI/RFI to ground so it doesn’t affect the DAC to begin with.

All of your arguments are around what ’shouldn’t’ be audible. Your comments are:

• "Concerns over picoseconds or nanoseconds of jitter are pointless when the requirement is ten thousands of times easier.."
• "Any argument that that these artifacts, existing 80dB, 90dB or more down, are audible are specious at best."
• "The devices ’wobble’ has to be pretty severe - defective - for this to even be part of the conversation."

Digital audio at an affordable level has sounded wrong to me until only about the last 5-8 years.  I’m only finding possible reasons to explain the deficiencies in digital audio that I’ve already heard for years.

"Cables make a difference by their ability to channel stray EMI/RFI to ground so it doesn’t affect the DAC to begin with"

ethernet wiring / cables are strictly controlled by certification / testing, in order to allow them in our homes/offices.. these cables are twisted per spec, to reduce RF noise below regulated values. on top of that, TX circuitry is limited to certain rise/fall time, balance params.