Here's my personal experience with the KEF R3's, I would likely qualify as an untrained listener, so take any impressions I present with credibility appropriate to that of a simple civilian that just likes high fidelity music.
TLDR; Almost endgame, but vocals were too recessed, which put me on the fence to return them. I finally got a UMIK-1 and used REW EQ. Now these are the best I ever heard.
Audio equipment I've own(ed) for reference: Philips x2hr fidelio, Beyerdynamic 1770 and 1990 pros, Neumann ndh20, Hifiman Sundara and Ananda, and SVS Ultrabook shelves. I listened to pretty much all genres, on Amazon Music HD Streaming -- some tracks go up to 24bit/192khz, but minimum was 16bit/44.1khz at least, so source used was better than anyone on this form can likely hear... All my Listening was obviously done with a DAC/AMP combo, but I won't mention which ones I used. I personally feel people that claim they hear differences in sound between transparent DACS are like people that claim they can tell differences between the same wines(
https://www.realclearscience.com/blog/2014/08/the_most_infamous_study_on_wine_tasting.html). The amp I used is 60W per channel and provided more than enough volume for my listening sessions.
Alright, so I had these for a month now, and they are an upgrade to my previous svs ultra bookshelf speakers. I listen nearfield in a small room with the speakers angled at 45 degrees. From the moment I first heard them, I could tell Imaging and Soundstage were without a doubt in a league above the ultra's. The separation of sounds in space are quite distinguished, and imaging is better than anything else I've owned or heard. I feel they disappear rather well, and much better than the SVS Ultras. The sound stage was also bigger, but I think there are speakers in this price brackets that have been quoted as going wider. Unfortunately I'm not a reliable source on the matter, but compared to SVS they go quite a bit wider, deeper, and taller.
For sound, the bass goes low in a small room, enough to feel it; 40HZ is audible for sure, and they do reach lower. I won't be needing a sub until I move out of my apartment. But for reference, I hear them going lower then SVS ultras, with more tonality and separation in the low end. It should be noted -- although the bass goes lower then the ultras -- the ultras had more punch. When listening to bookshelves, I get the impression of a center image bass, and in the SVS the impact was harder, but not as clean as the R3's. Mids were the reason I wanted to return these speakers. Center Image for singers felt recessed and they were too far back. They couldn't match the SVS's rather forward and elevated vocals I was used to. Except for vocals, I actually felt that the rest of the mid range was clearer in tonality for the R3's, same as the case mentioned in bass comparison. Treble is one of those regions I fined quite tricky to judge as my hearing caps out at ~15Khz. I will say the tweeter on both R3's and Ultra's extend quite well(likely past what I can perceive), and they contain all the details one would expect from HIFI listening. Few times, I felt that the treble was too elevated on the R3's while the SVS definitely had a significant percentile of tracks that I was turning the music down. I felt treble was almost perfect for my needs on the R3's, rarely harsh, but overall balanced, and detailed like my Ananda's. I did mention I own and listen to DT 1990 pros, but I only listen to those with serious reduction in treble as I find the Beyer 8khz peak murderous.
Finally Micro and Macro dynamics are also in a league above the SVS ultras. Listening to the Kef R3 for the first time, I finally understood what the term Micro dynamics meant. The R3 truly present small details with equal visibility to the listener as a lead instrument such as an electric guitar or center image singer. Macro Dynamics were also great with lows and highest retaining information.
I wanted to try the UMIK-1 mic with REW in hopes of fixing the deal breaker vocals. Here are my results, seems there are serious attenuations, between 150-200hz, and another at around 1Khz.
View attachment 102599
After generating the EQ pattern below,
View attachment 102600
Mids had gained that forward presence I learned to love in my old SVS ultras with solid vocal center image coming back to life. Bass seemed to improve as well and the treble was slightly balanced and then attenuated manually by me as it is my preference. Anyways, I love these speakers and will likely treat these as my end game for the years to come. Hopefully my raw experience is helpful to anyone reading this thread and looking for a perspective(non-learned) on the KEF R3.