Discerning a difference between streamers is difficult...only me or common for all?

I have no wish to add to the OP’s confusion, and I agree with many of the commenters who feel that past a certain level, streamers can vary in whatever added value they bring to a system. But we also shouldn’t overlook the differences in software. All these devices require some sort of operating system for connectivity, and most, if not all of them, are based on various versions of Linux. And within Linux there are a number of different playback and connectivity formats, among threm MPD, Minimserver, BubbleUPnP, Squeezelite, etc. All of these offer somewhat different sonic presentations. One reason I like my Pi2AES so much is that I can choose my own OS and player software. While a lot of these are free, like Ropiee, Moode or Volumio, I’m happy to pay extra for a system like Gentooplayer, which allows a wide choice of different "players" and a lot of tweaks and extras, like the Diretta ethernet protocol. Now there’s an extra layer or two of "tuneability." This isn’t for everyone, obviously, but it is worth noting that the software provided with a streamer can have a significant impact on the sound. It might consist of a basic DLNA server, or it might incorporate something more sophisticated.

I’ll list what I tried…

1. Mac Mini 2008 with its outboard power supply

2. Mac Mini 2018

3. Auralic Aries G1

4. Lumin U1 Mini

5. Bricasti M3 network renderer as Roon endpoint 

6. Aurender N200

7. WiiM Pro

When my 2008 mac mini crapped out and I replaced it with the 2018 version I noticed a slight degradation in sound quality. 
Bought Auralic Aries G1. Way better than Mac Mini. Lightning DS software was very good, sounded better using LDS than it did as a Roon endpoint. 
Lumin U1 Mini - slightly smoother sound than the Auralic. Hideous UI. Good as Roon endpoint. 
Bricasti M3 network card - virtually indistinguishable sonically from U1 Mini as Roon endpoint. Sold U1 Mini. Neither of these were any good as streamers. A cheap Audiolab 6000CDT transport spinning CD destroyed Roon. 
Bought Aurender N200 to try. Stands up to and in most cased exceeds CD quality streaming CD files and hires Qobuz. Much better than Lumin U1 Mini and the Bricasti M3 network card. Tried it with Roon and prefer the sound of the Conductor app/processing. Solid, stable and great sounding streamer. Sold my very decent analog setup as I just stopped playing vinyl records - streaming sounds excellent!

As to WiiM Pro, I tried it and returned it. Sounded like 💩

So my experience differs from some in this thread. Oh and I’ve used the Aurender with 3 different DACs, with Pass Labs separates and 2 different integrated amplifiers. No issues with sound quality. Natural, detailed, engaging presentation. 
 

Some excellent comments above. Could it be the room? Could it be your connects? Is your Ethernet filtered? Power treated? All the stuff that goes with streaming needs to be cleaned up. Lots on Agon on how to do it.

Why not a Innuos Zenith mk3. It has a cd ripper ,a Nice SS drive  fantastic interface 

3 separate LPS power supplies ,isolation damping everywhere including the Teac cd ripper and SS drive,and excellent iso bearing feet ,and the Excellent  Mundorf Mlytic  capacitors , plus the innuos sense app is very intuitive .

the  Zen with reclocker sounds actually a bit better ,

i use my own Gaia reclocker , the sense app puts folders and playlists together seamlessly and sounds better then Roon which is a big bonus setting up judt hit the app button found and yiu just pick configurations the  most thought out streamer 

I have found to date and this is a bit warmer sounding due to the Mundorf caps .

tip if you want your digital to sound better still Tubulus Audio cables ,they beat cables much more $$ and only true I2S  -Audio cable  the AQ dragon audio only exception ,and the less expensive Tubulus Concentus is much better. And Ethernet cables very good ,always put your best Ethernet cable at your end point- Streamer 

land Router put a good LPS to block incoming noise,Thst cheap wall wart judt ads noise to your audio chain,digital house to house is not grounded !                      Linear Tube Audio-  excellent LPS for $750.

streamers don’t have a sound or different tonality (assuming no differences re up- or oversampling, etc.).  They have different levels of noise, but even there, the differences between relatively cheap but well-engineered streamers and insanely expensive ones can be subtle or nonexistent.  Noise levels can affect how well you’re hearing your DAC, but if it’s a decent streamer, your DAC dominates what you hear.