Update:
After probably 100 hours of reading reviews and spec sheets for a wide variety of speakers, I decided to try the LS50 Meta first. The R3 is second choice, followed by the Ascend Sierra 2EX.
The deciding factors were:
— Better imaging.
I read three reviewers who gave detailed and explicit descriptions of the precise imaging produced by the Metas.
Other reviewers also commented on the imaging. One reviewer said the Meta imaging snapped into place better than the R3.
These comments on imaging were in the context of high praise for the tonal quality.
True, some preferred the tonal quality of the R3 in the mids, but the difference was slight.
Bass is not likely to be much of an issue, as I will cross the subs at 80 Hz, or 60 Hz if that sounds better. (The L12 subs have filters at 60 and 80 Hz.)
https://www.stereophile.com/content/kef-ls50-meta-loudspeaker
https://thenextweb.com/plugged/2020...grades-an-audiophile-fave-to-near-perfection/
http://www.audiodrom.net/en/stand-mount-monitors/detail/29-stand-mount-monitors/714-kef-ls50-meta
— Lower distortion.
From 300 Hz to 10 kHz, the LS50 Meta spec is 0.1%; 175 Hz to 20 kHz, 0.4%.
The R3 is 0.3%, 130 Hz to 20 kHz.
For most of the range of interest, the Meta is 5 dB better than the R3: -30 vs -25 dB, respectively. (Correct me if I did the calculation wrong.)
It seems strange to spend $1700 on the miniDSP SHD and Hypex amp to minimize distortion below the audible range, and then throw away a whopping 5 dB of distortion in the audible range in exchange for small and subjective differences in tonal quality.
(I'm guessing that the lower distortion contributes to the better imaging.)
— Overall, I felt the LS50 Metas would be best suited to my small room.
The speakers will be 6 feet apart on a 12 foot wall. Greater separation is not possible due to an inward swinging door. I'll only be 6 or 7 feet from the plane of the speakers. I won't need the power of the R3s. And, it may be that the LS50 sound will be better integrated at my ears without the vertically separated mid speaker of the R3. (I reverted to the larger room, having acquired sufficient WAF to swap some furniture between rooms.)
The LS50s arrived yesterday. I hooked them up to the existing Onkyo integrated amp (100 watts per channel), and set them in the living room. That room is twice the area of my room, and is missing half a wall. I could definitely hear the difference (compared to the old Q15s) on all the CDs I played, but I wasn't thrilled. When I put John Williams' Romance of the Guitar on, I was struck by the presence. Really, really nice. Michael Murray playing Bach on the Methuen organ was very good, too. I'm hopeful that when the full system is set up in the room, and I play newer recordings (or maybe just better set up recordings) many of them will be as impressive as the Williams.