I am not a high volume listener. Medium level has always worked best for me. I also found British speakers a long time ago. Low efficiency, high accuracy. Warm smooth sounding with incredible sound stage and imaging.
I started with KEF and for years thought they were the best. I have tried other manufactures over the years; Magnepans were very nice but are quite unruly in my small room. I have heard about them for years and I finally tried Harbeth in my home. They very much are the current holder of the crown of the British sound in my view. Amazing speakers and still hand built in England!
One caveat is that these type of speakers really appreciate quality amplifiers. I certainly don't mean how much power, but high quality power. I have tried several; some of my favorites have been T+A, MBL; ARC and Audio Mirror for tubes. My favorite over many years of trying others is McIntosh.
I have found that McIntosh and British designed speakers are a match made in Heaven! I believe that my McIntosh amplifier and Harbeth speakers are a tremendous combination for low to medium listening levels. They definitely can get up and run at a much louder level, but I rarely play at those levels.
One component that I believe is very over looked in this discussion is the pre-amplifier. Over the years I have found that the pre-amplifier makes huge differences in all volume levels, but especially in low volume listening. I have tried and personally believe that counting on a source component such as a DAC or Streamer as your main control unit, even if digital is your primary source, is a big mistake. A quality pre-amplifier affects the over all performance of your system as much as almost any component.
For tubes the finest I have tried is ARC and McIntosh; solid state, which is my preference, there are two that have stood out for me. McIntosh is my favorite both in functionality and performance. There is very much something to be said about synergy between your amplifier and pre-amplifier. The other is the surprising and amazing Wyred 4 Sound STP-SE Stage 2. The Wyred is fantastic, but the synergy of the McIntosh components won out for me.
A good friend of mine has recently replaced his tube amps and pre-amplifier with Luxman solid state components. These are top notch rated components and he feels they are fantastic. I have not had the opportunity of listening to these in my home, but I am confident they would work very well with my Harbeth.