speaker upgrade fever

Harbeth and Joseph Audio speakers share some similarities, but are also very different in some ways.

They both do imaging and soundstage very well and are fairly neutral.  Harbeths are less detailed.  Your KEF Ref 1 speakers have more detail than any Harbeth I've owned (I have not had the 30.1, which I think is what you meant you are considering).  The Kefs are also a little bit warmer, Harbeths (depending on the model) can get a little hot at the top end when pushed.

The Joseph Audio speakers will be more detailed than the KEFs or Harbeths, and will have better imaging, to the point where it is almost clinical, as in the instruments and vocals are very defined in space.  I really like this, but there's the possibility of being drawn into the presentation versus being drawn into the music, which is where I think the Harbeths excel.  

I have listened extensively to a friend's system with the JA Pulsar Graphenes and would take those over KEF Referency 1 or any Harbeth speaker I've heard.  I have owned Harbeth Super HL5 Plus, Compact 7, and P3ESR.  I loved them all, with the last two being my favorites.  The same friend that has the JA Pulsar Graphenes also had the Harbeth 40.2.  I remember when he told me had moved on from those, I thought he was nuts.  Until I heard the JA Pulsar Graphenes in his system.

I'm an ATC active owner and Focals. I run my atc w Tubes. For me it's tbe perfect balance of detail and musicality. The focal paired w Naim is also unique but the speakers can be interpreted as bright. So I mention my setup for refrence... however if I was interested in moving slightly away from detail to something forgiving and evwn more musicality... Sonus Fabre are going to be my go to. They are gorgeous.... to be honest if I was starting from scratch and trying to decider my setup or SF I'd be torn... I'm already completely committed w Rel subs too and I love my system so I'm not considering anything else. But SF r very impressive for my taste and slightly different flavor. Plus they are gorgeous looking speakers especially in tower. Just a heads up... in tower you sacrifice imaging. I've heard SF bookshelves and they are loud and deep w bass very impressive, I even asked if they had a sub hooked up in which they didn't. Never heard speaker imagine like SF. And if you wanted to add more bass you could c9nder a pair of Rels and maybe have everything you wanted in that setup. 

One last set of advise, if your have tubes I highly recommend NOS tubes. I run 1943 Ken-rads amd I found these to be the best tube nee or old. Deepest bass of all tunes new or old and rich thick mids. And didn't loose any details in tbe highs. Thought I'd mention that. Best of luck

Lots of good brands that will work.  Your amp has good power.  I think I have seen Vandy 4 used for about 10k or so.  Otherwise I would just repeat other recommendations 

I am the very-happy owner of the Linkwitz LX521.4 system for almost 10 years now. For me, this is my end-game: the spacial and  smooth presentation across the entire frequency band is to die for. You can see my system here: https://linkwitz.store/blog/2023/01/20/new-linkwitz-lounge-in-fremont-ca/

I am NOT a dealer by any means: I agreed to open my home to interested audiophiles, because I am convinced that - once you hear it for yourself - there is no going back to anything else, particularly in this price range. If you are good with your hands, you can built those from an IKEA-like pre-cut flat-pack (that's what I did), saving you about $5K (and have your choice of finish: mine is Lexus Pearl White automotive coating). Note, however: you will need to buy the entire system, including the two PowerBoxes: each Linkwitz driver has its own (ClassD, Hypex N-Core) amplifier, 5 per channel (250W x 2, 200W, 150W, and 100W for the tweeters), which comes to 10(!!) amplifiers total; moreover, each channel has its own active crossover, making sure each driver operates only in its linear frequency range. As said above: the result is a mind-boggling being-there illusion. All you need is a good preamp/phono stage (if you spin vinyl) and/or DAC (I use the impeccable MSB), and you are ready to go. I use a tube preamp/phono stage (Supratek Grange), which gives me the best of both worlds in terms of smooth mid-range and punchy authoritative bass. If you happen to be in the Bay Area, feel free to set up an appointment!

If you are looking at the Vandersteen treos, I’d suggest you listen to the Vandersteen Quatro CT’s. Which have better bass and great self amped subs in them already. I think you can find for &14,000 used. Which is a bargain.