Anybody want a laugh?

Kyle would be proud!

I have no idea whether this modified switch will reduce audible noise on a stereo system. However, EMI/RFI noise is a major issue in building physical networks. Here is a link to a Cisco switch install guide, read the part about EMI/RFI. Note this section is included in all Cisco data center-grade switch install guides, because EMI/RFI noise produced by switches is both real and sometimes does interfere with the signal. 

https://www.cisco.com/c/en/us/td/docs/switches/lan/catalyst4900/4948E/installation/guide/4948E_ins/0...

There are many ways to reduce and suppress this noise - installation methods, shielded cabling, filters, etc. One proven way in electronics design would be to replace lower-grade capacitors with noise suppressing capacitors. Here is an example of a capacitor design that reduces EMI/RFI and would have a measurable reductive effect on noise levels if installed into a Cisco switch:

https://www.illinoiscapacitor.com/pdf/Papers/EMI_RFI_suppression_capacitors.pdf

The OP could be correct that the modifications made to the referenced EBay switch will make no audible difference. But, there’s no way to know without actually testing the original and modified devices. 

However, the OP and some other posters are quite incorrect in asserting that switches don’t pass measurable EMI/RFI noise along with the signal - they do, as Cisco warns in their install guides. And, they are incorrect in asserting that it’s not possible to measurably reduce that noise with potential for an audible effect - Cisco gives us a few tips for how to do it, and we know that noise reducing capacitors are routinely incorporated in electronic designs for this exact purpose. 

Phasemonger

Like everything audio, visual or taste just listen, view and eat and determine for yourself if you like what you hear, see or consume. That simple. The rest of this arguing and name calling is a complete waste of time and off topic. We are all big boys and girls and can make our own determinations based on our individual senses. Others can’t tell me if I will taste or hear a difference I like and enjoy. Only I can do that as my senses are mine, not theirs. We are not all exactly alike in terms of sensory functioning and in the case of Audio our systems and rooms are completely different.

So simple folks and the only way this falls apart is if someone has not listened, viewed, or tasted, but feels compelled to make judgements anyway plus save me from myself. That my fellow Agoners is not funny, but rather nonsensical.

Newsflash! We humans don’t know the why of most things in this world and we see our ignorance in the rear view mirror of life.  Most often long after we pass away. 

I read the part about EMI/RFI noise produced.  I paid particular notice to this and what followed.

The Federal Communications Commission (FCC) publishes specific regulations to limit the amount of EMI and RFI emitted by computing equipment. Each system meets these FCC regulations

It  warns about bad wiring practices. It is talking about installations in enterprise closets full of equipment. Lightning protection , ventilation, humidity  you know thing to worry about in a high traffic business environment not someone's home system with a couple of end nodes. 

This particular switch is nothing but a $40 Cisco unmanaged layer 2 with a couple of meaningless "upgrades"  there is nothing this thing will do to an audio signal that's audible. Evaluating these types of "tweaks" for that's all they are, by plugging it in trusting your infallible senses and saying "wow it's amazing " is a meaningless gesture. It's like eyewitnesses who manage to trust their eyes but usually get something wrong or wine tasters who can't tell red from white when the white is dyed red. People need to get over this hubris that they are infallible and their senses are not subject to normal human biases. 

The white paper linked to earlier is another attempt to wow with nonsense. It talks about line jitter leaking into your DAC and causing all sorts of nasties. So they use very precise clocks to control this. Only problem with this fix is ethernet line uses a 25MHZ clock, yeah megahertz . So it’s "fixing" a nonexistent problem. Not to mention the "line noise/jitter" and clocking doesn’t reach to DAC, the packets are stripped of the outer layers and any clocking of the stack by software, processed by the software in the streamer to retrieve the data, placed in a buffer then the DAC clock asynchronously pulls the data for conversion. The bottom line is with today’s software, hardware, filtering and precise clocks placed close to the DAC the last thing you need to worry about is a switch. I also find it amusing why no worry about the little $100 modem that converted the incoming analog signal to your house and built this digital signal so your devices could read the signal? That has more to with what’s going on with your streaming than any switch you place downstream. By all means decide what you want, buy what you want but try informing yourself as to what you’re buying and use some common sense.