Why do I need a switch?

To your question, you don't need a switch, and you don't need fiber.  The signal is the signal, so that doesn't change.  The starting point is to connect your Ethernet cable to your streamer and listen to music. From there, if you wish, you can explore the many products designed to "enhance" your digital music experience.  These products generally claim to either remove noise alleged to ride on the Ethernet cables, or to reclock the digital signal thus sending a signal with lower jitter to your DAC.  These range from different cables to switches, to filters, to reclockers, to digital-digital converters (DDC) that buffer and reclock the signal and also allow different formats of digital inputs and outputs.  

Switches can have clocks, such as the English Electric 8 and Bonn Silent Angel N8 switches discussed in this thread, which are both essentially the same switch from the small OEM manufacturer ThunderData, in Guangdong, China company.  They both have the same board inside and both have an added TCXO clock.  My understanding is that the English Electric switch has a fancier case and feet.  There are even more expensive switches you can purchase with one of the top-of-the-line switches being the M12 SWITCH GOLD, by JCAT, for €3,800.  Silent Angel has a Bonn N8 Pro switch, which is supposedly better for audio (BTW, the new fad is to put "PRO" behind a product's name to indicate an upgraded, better quality, and more expensive model).  Here is an article about switches from two years ago.

Regarding fiber, that is simply a method of providing optical isolation for the purpose of reducing noise.  As stated in this thread, you can do that with two $25 converters and inexpensive fiber cable.  However, be aware you are adding two noisy SMPSs with those converters, unless you also splurge for a couple of LPSs at around $100 each.  You can also do it by using the GigaFOILv4, which would require only one LPS.  I have both the fiber/converter set-up, and the GigaFoilv4, and I have tried both, including the LPSs.  My run is 45 feet from my router to my system and I have both CAT8 Ethernet and fiber cables permanently in-place, so I have conveniently tried A/B comparisons between the two over a longish period.  I seem to detect a slight difference in the sound but ended up prefering the CAT8, at least with my current set-up, although YMMV.

Whether any of this changes the sound of your system, only you can decide and, unfortunately, only by listening, not by reading these forums which are great for learning what is out there but not so great for evaluating the actual sonic impact of this stuff.   In my system, none of it makes a profound difference but maybe a little so I am using a bunch of stuff, nonetheless.  IME the components you are using (i.e., streamer and DAC) have a much greater impact on the sound than cables or add-ons.  Below are the ancillaries I am using:

• LPS on both modem and router
• 45' of CAT8 into dual Bonn N8 switches with two LPSs
• muon network cable/muon filter into server
• muon USB cable into DENAFRIPS Hermes DDC
• TWL AES/EBU into DAC

Good luck.

@erik_squires we have gone through this, there are no such thing as “hospital” grade Ethernet. That is flat out false. What you are talking about is a device that is meant to filter current leaks in extreme scenarios for life preserving equipment and these devices are old and don’t have this already built in. It is the failsafe when someone connects the Ethernet cable to the AC outlet. Under normal operating conditions it does not do anything at all, it is even says that in the specs you share.

@markprice i am perfectly happy not being fooled by snake oil salespeople. You do you though.

@fredrik222 Yeah, you also don’t believe in published standards, so you we did go through this and we decided you didn’t know what you were talking about.

Interesting you are changing your tune now, a month or so ago you assured me there was no reason for them ever. Now you are saying there is. We’ll get you there.

Under normal operating conditions it does not do anything at all, it is even says that in the specs you share.

I’ve never claimed it did a thing for audio. :) What they do, which is useful for me, is add about 4kV of breakthrough voltage, forcing potential surge currents to find a path upstream instead of downstream.

OP - Do you have a CD transport? Have you compared the same title/version of a CD with the streamed file to see if you can hear the difference?

I am streaming with my ASUS laptop gaming computer hooked up with an inexpensive USB cable to my PSA PerfectWave Mk II DAC. The computer is receiving its signal by WiFi. According to conventional audiophile wisdom, this setup should sound terrible.

I also have a PSA PerfectWave Transport hooked up to the same DAC. If I play a track from a CD and then stream the same version they sound identical. I have done this at least a dozen times and the results are consistent.

Does anyone think that the streamed track will ever sound better than the same track played from a CD (through the same DAC)? Every time I read reports of our audio brothers spending thousands of dollars on digital tweaks I want to know if they have ever compared their streaming setup with the corresponding CD. Does their streamed version sound clearly inferior to the CD? Is this why they are adding hardware, cables, and expensive streamers to their system? After they spend the big bucks, does their streamed music sound better than the CD?

CD playback has been optimized for sound quality for 50 years. It is relatively simple and straightforward compared to streaming. They both play the same original file. The difference is that the streamed file has been folded, stapled, split apart, knitted back together, and abused in countless ways before it reaches your DAC. Can anyone explain to me how a streamed file would ever sound better than the original CD played through the same DAC? When audiophiles spend tens of thousands of dollars on their streaming setup are they simply trying to match the quality of playing a CD through a decent quality transport? If that's the case then why did they go with streaming in the first place if they really care about sound quality?

Before you spend the time and money tweaking things like digital switches, my recommendation is to get a handle on how your streaming quality compares to CD playback. If you don't have a transport you can pick one up for a reasonable cost. Then, if you decide to add esoteric digital equipment to your streaming setup you can check the SQ effect with each "upgrade." My guess is that if you do this you will quickly find that the digital signal is quite robust and that if you compare to a standard (CD playback) you will determine that adding things like switches don't make a perceptible difference.

Using some sort of control - in this case CD playback - is critical to making SQ judgements IMO.