To address what I don’t like about the Harbeths, that would cause an upgrade "itch" to be scratched? It’s hard to say - they do from time to time sound a bit "boxy" on big, orchestral stuff.
I understand what you mean about the "bit boxy" thing.
I LOVE Harbeth speakers. They are easily in my top favorite speaker lines, for essentially the reasons they have their fans: that rich, organic tonality and even top to bottom balance, clarity without fatigue, etc.I’ve listened to the whole line up, and heard the 40.2s do astonishing things. The Harbeths disappear far more than you’d expect given their old school "boxy" look.
But while they do an excellent disappearing act, that isn’t their strongest characteristic. It’s bettered by other speakers, the modern designs that go for heroic attempts at reducing cabinet noise etc.
I had the big Thiel 3.7 speakers and was looking to see if I could downsize a bit due to some aesthetic / ergonomic issues. I actually bought a pair (used) of Harbeth SuperHL5plus speakers and lived with them for a month or two. They were fantastic in all the ways I’d heard from them before: open, rich, organic, sparkling highs without fatigue, so balanced and controlled from top to bottom, and special with vocals - the way they fleshed out the human voice in such a human way.
However, I found when comparing to my Thiels, which are of the "low cabinet/low coloration" school, the Thiels seemed to do almost everything the Harbeths were doing, but better. They had a rich, full quality - e.g. acoustic guitars had wonderful full sized body - and a similar organic realistic timbre to acoustic instruments and voices. But the sound was just that much more clean and precise and hence realistic. So for instance, playing tracks from the Los Angeles Guitar Quartet, 4 classical guitarists playing at the same time, both speakers had beautiful tone and sound very similar, but compared to the Thiels there was an "extra" bit of tone in the Harbeths, a bit of "hearing the box" added, making for a bit of blur in between the guitars. Where the Thiels seemed to clean up everything around the guitars, for a cleaner more precise and live and realistic presentation.
So I think the Harbeths beat plenty of speakers on their wonderful tonal quality and balance. And I’d take them over the majority of speakers out there that I’ve heard. And their balance of box vibration is so canny that you don’t necessarily notice most of the time and can even add to the richness. But in direct comparison with even more precise speakers, it might make you itch for more (as long as those other speakers can compete well enough in most other areas of tone with the Harbeths).
In the end I sold the Harbeths and kept looking. Still, they were so good with voices they haunt me, and I’d love to have a pair of Harbeths still around to throw in my system.