I do agree with @Jesus_Rodriguez here. Even though I’d love to agree wtih an article that puts Roon in a favorable light, I’m unsure what’s going on.
That said, I am willing comment on this why they might sound different: people hear what they want to hear.
If you get the bits to the microRendu accurately, and you do it in a way that pulls the content so the device owns the clock (Roon Ready, UPnP, and “bit-perfect HQP NAA” all pull in the only way that matters), and the bits are the same, then all should sound the same.
There are complexities here, but it’s all completely unknown without real forensic analysis … which no one is doing.
Finally, the reviewer in this case states:
After about a month, I switched over to the Roon protocol, simply by downloading and installing Roon on my Mac Mini, and switching over to the Roon app on the microRendu. The last piece of the puzzle was getting the Roon app for the iPad Air. My overall impression is Roon was slightly superior to DLNA sonically. It was not a landslide, there was just a bit more refinement to my ears. This may be due to the way Roon supposedly simplifies the audio chain, as many claim DLNA is a complicated protocol. I stuck with Roon, and continue to use it.
(I’ve bolded the part I think is most important)
When I read this, I take this meaning “The experience was better with Roon, the sound was still perfect, my overall happiness was greater, it might be ears or my brain but i don’t know… I just know I like what I hear… I’m sticking to it.”
The best thing is to take all reviews with a grain of salt and try it out yourself.
The microRendu does a lot of great things that are well known to lead to better audio reproduction.
Try it out! It is an awesome product and I doubt you will feel any other way about it yourself once you’ve lived with one.