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

When I purchased my Rockna Wavedream Signature DAC, I saw many owners recommending pairing it with the Rockna Wavedream NET for best results, that the Rockna server took things to another level and that using the i2s connection was critical.  

Prior to the Wavedream NET, I had a Roon Nucleus.  If there was any difference in sound quality, I couldn't detect it.  The Wavedream NET is a nice server and provides functionality the Nucleus doesn't, most notably, an excellent CD transport is included.

On another note, I initially used a DH Labs i2s cable, but "they" said you need to get a Tubulus or RAL i2s cable (or something even more expensive) to get the best sound quality.  I purchased a Revelation Audio Labs Prophecy CryoSilver Reference I2S Cable and was able to A/B, as the Rockna Server and DAC both have two i2s connections and thought the RAL sounded better than the DH Labs cable, but I recently did that again and couldn't detect any noticeable difference.  I'm not sure if that was confirmation bias initially, or that my ears are getting worse, or something else.  I have been told by other audiophile friends that I have a "good ear" and my system is pretty revealing, so I'm leaning towards confirmation bias.

The DAC is where almost all the magic happens.  Focus on getting that as good as you possibly can and then tweak away. 

I am surprised so many don't hear a difference in streamers, particularly comparing those with big price differences.  I wonder if "noise" might be veiling the differences.  EMI, RFI, ground plane noise and jitter are like grease on an optical lens, it hides the difference in a cheap and a quality set of optics.  After significant upgrades to my DAC and Streamer I still noticed a level of glare and lack of resolution that responded favorably to extensive noise control.

I also agree with @mitch2 on the effect of the Sonore SignatureRendu.  I was using an UltraRendu to utilize the Ethernet output of my streamer which I preferred to USB.  Replacing the UltraRendu with a SignatureRendu was a WOW moment.  Of all the upgrades and changes I have made the SignatureRendu takes the cake.

I’ve heard bigger differences between music servers than DACs, with the exception of when I had the DCS Rossini APEX DAC.

I heard noticeable differences in SQ among three modestly priced but capable streamers: CA MXN10, IFi ZS and Wiim Ultra in my humble system.  All were tested with an external dac.

@lanx0003 What was your opinion of the Wiim Ultra?  I snagged one on a black Friday deal.  It's for my son for Christmas.  I was impressed by the size and weight of the box (I haven't opened it). I expected something much smaller and lighter.