Back in the mid 70's, we'd demonstrate and sell Crown amps exclusively with big IMF's. One or two here sneer at them but Ken Rockwell measured a few including the preamp (fingers dowen a blackboard sound was one audiophool comment when ARC sludge-box preamps became the sonic rage) and they still hold up very well half a century later and what comes out is basically what goes in! Four ohm and below drive is difficult for the smaller models though as protection kicks in.
I repeat, the M30's have changed out of all recognition from the BBC drop-in replacements of the model measured here. The Beeb have gone over to active Dynaudios mostly it seems for general 'noisebox' studio reproduction (I was told the odd Genelec is around). Now the M30 range is basically a domestic model, the response has flattened noticeably away from the LS5/9 donor model (which is still made by companies wanting to cash in on the legacy - the Rogers one looks awful in a HiFi News test and the Graham version is ripe and dull in balance if a HiFi Review squashed plot is to be believed). Below how the BBC wanted their two main monitors balanced - the M30 in original form smooths the highs a bit. I believe it's 5dB per major division. My Rogers 5/9's definitely sounded either mid-bass 'tubby' or 'laid back with sharp toned highs' depending on the room.
Below the Graham as measured in HiFi Review. Note the upper hundred Hz suckout.
The current M30.2XD isn't subjectively as bad as this although for myself now, I was staggered how much better over the previous model the slightly larger C7-XD model is, the mid bass under perfect control in the lengthy session I had with it.
I just hope people here can accept that any manufacturer should be allowed to learn from and further develop their products as the years and decades go on. Some makers regress sadly, but in my book, current model Harbeths seem excellent for the market they're in (which isn't necessarily 'ours'), the sound is perceptually their clearest yet (hell, I'm going to say all but on a par with many active models) and priced mainly to compete with now inferior equivalents from their 'BBC Legacy' competition, of which three well known makers immediately come to mind, either regurgitating old relics of the past, or trying to move on but with uncertain future now their final designer link with the past has moved on.
P.S. Rogers 5/9 measured in HFN - no idea how that terrible response equates to a similar sweep done on a Klippel - HF seems higher than ever in these...
https://www.hifinews.com/content/rogers-ls59-classic-se-loudspeaker-lab-report