Auditioned some speakers ~£800 (KEF, Monitor Audio, Rega RX1, Dali)

No but I'm sure it's in my future!

 

Surprised on your impression of the RX1. I don't hear the Rega speakers as dull (I've owned/own the r1 and the RS 3). The 2 online reviews I've seen on the RX1 describe it as quick coherent and involving, but maybe a little light tonal wise. I think that's about right.
Monitor audio, I own a pair of older mini monitors and they are detailed and can be bright. Amazing imaging (better than the LS50).
LS50 is a good speaker but fairly low efficiency with a complex impedence. The bass is deep for a mini, not as well defined as some other small speakers I've heard, It's a hair bright on top, accentuating vocal sibilance more than some others, the mids are very nice, slightly metallic and shiny at times (a trait I hear in all metal drivers). Kef did a pretty good job at that price and size range.

 

The Rega mono amps should drive them like a champ, of my amps, overall the Elicit (version 2? the one before the current R version) works the best, but sometimes feel they would do better with some more power, Rega said the exon will drive "the most awkward speaker loads" in the product brief. The LS 50 might not be the most awkward, but it is not an easily driven design. I wonder if Rega will ever make separates again.