Is there a point of diminished returns with amps and Harbeth 30.1s?


I’m currently using Herron M1As with my 30.1s and I’ve upgraded the rest of my system (Aries/Fatboy/SUT/DL103r and Lamm pre and phono) and each upgrade has been VERY satisfying. So is it going to be worth spending $5000 or so on the used market to upgrade the Herrons? Any thoughts as to whether I’ve reached the apex of amp/speaker performace for the M30.1s?
dhcod
@dhcod - Just remember that it doesn’t matter what anyone else hears, claims to hear or claims to tell you what you should hear. All that matters is what you hear in your home, in your system. Then you can relax and listen to beautiful music while others are too fired up trying to push their views onto you. I was a conservatory-trained musician in my youth and one thing I learned is not to assume someone else cannot hear something that you can’t.
Thanks @chayro! I’m plenty old and have been doing this for so long that I do know that. Also work tangential to the music business (feature film editor) and I have conversations with mixers and engineers all the time about how we all hear differently!
first i will say harbeths are excellent speakers, even great speakers

that said, the man behind the company is a first rate capitalist (no shame in that), uses many modern tools of marketing to maximize economics of his venture... including setting up a ’user group’ that effectively sings praises of his products (and quashes negative comments by and large, as well as useful discussions of ancillary gear)... he personally ’moderates’ the group, and posts actively as a participant, so it is heavy hand employed there

as for the ’offer’ of a blind a/b test, it would have been one that he controls, so grains of salt taken there

finally, a few years back, i have personally (with help from my son and a good hifi bud) done a blind a-b-c test, which took some doing, with my son doing the switching and db level match, using two sacd tracks - comparing an audio research vt-50 tube amp, audio research 100.2 solid state unit, and a w4s class d st-500, running into harbeth shl5+’s ... we could pick out which amp 6 out of 6... treble detail and imaging was different, bass tightness was different, midrange articulation was different...

bottom line, excellent speakers, pedantic and self serving owner, the user group is kool aid drinkers only (dealers, inexperienced or lazy fanboys), other discriminating, experienced, intellectually honest/curious folks usually find the b-s factor too high to stomach
I’ve never really understand the usefulness of blind tests. Do people actually know what they prefer in a short listening A-B session? It takes me a week of listening to determine if I like the sound of a component, unless it’s truly horrible or completely mismatched. I’ve fallen in love with many things upon first listen…. only to want to hang myself for a stupid purchase a week later. 
The amplifier thread on HUG (!) is interesting if only for the remarkably *wide* range of amps that owners are using with Harbeths.

I think the company went over the edge in the issuing first of the Anniversary series and then the XD series, both of which entailed very large price increases, one on top of the other.  I'm just glad I snagged my (regular) 40.2's when I did.