speaker endgame upgrade recommendations coming from Harbeth C7ES-3 XD2?

   Among conventional box speakers, you have two basic camps—modern “high-tech” speakers using technology and modern materials to kill resonance from drivers and cabinets and those who employ resonance even if this is “messy” and does not measure well.  Many British Isle manufacturers are in the “messy” camp, like Harbeth, ProAc, Graham, Tannoy, and Audio Note.  In the USA, companies like Devore and klipsch have models in both camps.  
   I tend to like “messy” speakers more because they sound lively and musically natural.  I don’t care that much that bass tends to be not as tight or extend as deep.  A lot of modern speakers in the other camp sound dead and need to be played at higher volume levels to have some life; “constipated” is another term used for that sound. 
   My other preference related to lively sound is higher efficiency.  Many of the fery best amps are low-powered and high efficiency helps with finding a good match. 
   For specific recommendations, it is hard to say without more details on budget, room size, speaker location limitations, etc.  But for a rough guess, I would suggest Volti Audio (quite good horn-based systems), Devore, Audio Note, Graham, Fyne, Charney Audio, and Songer Audio.  
   A dealer in my area used to carry both Harbeth and Audio Note speakers.  I found it interesting that most of his new, walk-in customers came to hear Harbeth, not Audi Note and many did buy Harbeth, but of those customers who listened to both brands, many switched to Audio Note; there were not many coming in for Audio Note that went the other way.

The drivers on this cone-based speaker are unique and, in my opinion, better than Beryllium based drivers. Same detail but no harshness. It is my end game speaker so much so that I tossed the shipping boxes a few years ago. 

Yamaha NS-5000PNST 3-Way Bookshelf Speakers with Stands | Hi-Fi Heaven

Yamaha NS-5000PNST 3-Way Bookshelf Speakers with Stands | Hi-Fi Heaven

Spend the saved money on a top-class powerful amp for these speakers. 

Ive owned too many box speakers and several OBs. I much prefer OBs whose money goes into part not coffins

I had a pair of Harbeth 30.2 XDs for a number of years, but ultimately upgraded to Joseph Audio Perspective Graphens. I am fairly sure the Joseph's are in your price range.

While the Harberths produced the kind of accuracy and transparency I value, the Perspectives take both of those to the next level. They are considerably larger than the Harberths and the resulting bass performance is notable. But for me, it is the fluidity and detail that have made the difference. 

The good news is that in the $20k price range, you have an enormous range of options, probably too many if I am being honest. Hearing more about what you listen to and source would be helpful, but in the end you will want to spend some time listening in person. 

Good luck with your search!

@audiocanada I was thinking Tannoys, Fyne Classic Series, even maybe Klipsch Heritage, Devore O/96, a friend also recommended active ATC’s and Dynaudio Confidence

As you already discovered, the best option is to demo yourself as sonic preferences are personally subjective. 20k is a substantial amount to spend. Also, depending on the design, tube amplification is usually more musical than SS.

Since you like Harbeth, climbing to the 40 would be a good bet. 

Since Fyne was started my ex-Tannoy engineers seeking to be unshackled, I consider their offerings to be superior to Tannoys. At AXPONA 2022, the Fyne Audio F703SP sounded great - I could live with their sound. Demoing several Tannoy models I didn’t care for the sound, sounded subpar to modern offerings at audio shows and stores.

Volti Audio speakers are superior to Klipsch Heritage as Greg Robert’s designs his speaker to complete directly with Klipsch. Both brands are highly efficient, usually low watt tube amps are used with them. The Volti Razz sounded clear, clean, and effortless at many audio shows. I own the Volti Rival. I choose the 100db Rival to investigate tube sonic magic starting with flea watt SET Amps. While not sterile, both are more neutral than the more musical Harbeths. Amplifier low power requirements should be considered.

The Devore O/96 and the Fleetwood DeVille are the most musical speakers I’ve ever demoed at many audio shows and audio stores. If maximum musicality is your goal, then I would go with the O/96 as maybe the safer bet as many more are sold. The O Bronze is a significant sonic step up, but at 30k out of your budget.They are efficient are are typically matched with tube amplifiers.

I hoping to acquire the musical O/96 to compare to my more neutral Volti Rival during my low watt tube amp adventures - what fun!

ATC sounded great at audio shows. I’m not familiar with Dynaudio Sonics, maybe I don’t recall as there are many great sounding speakers (do things well) at audio shows, but I’m searching for Sonics that subjectively resonates with me.

Good luck.