What Horn loaded speaker/ speaker system for $10k'ish and under

How about a pair of used Avant Garde Duos? 

Hello Sir

I personally own 26yo JBL S3100s a 2 way asymmetrical horn design with a 15 inch bass driver. They will not thunder you out the room, but give very fast bass response especially for a 15 with 94db efficiency without the horn drawbacks. The ME150HS bass driver is basically a 600 watt basket with a 2235 cone. You will not hear much talk about them as they were designed for the Asian Market even though made in America. Mine have been used with multiple amps throughout ownership, but settled on Warner Imaging ER300s a small manufacturer based in Baltimore around 2000 who knew how to build solid state with "Tube Character". If I decided to give them up I would replace with 4344Mk2

https://www.canuckaudiomart.com/details/649479281-jbl-s3100-minieverest-rare-in-northamerica/

https://audio-database.com/JBL/speaker/4344mkii-e.html

I have a pair of JBL 4349's in my main 2 channel listening system which use a 12" woofer and their relatively new waveguide design with a 1.5 inch compression driver for high frequencies.  I thoroughly enjoy these speakers and the high frequency response and tonal qualities of the waveguide are delightful.  They have no harshness and are not bright.  Smooth response, great soundstage/imaging and are very detailed cabinets.

Low & mid frequency response of the pulp 12" is also very good, though I cross over at 70 hertz to JBL subwoofers.  The few times I've used them while bypassing the subs, I've found the 4349's to have nice, detailed, firm bass response and may be more than adequate for most listeners.

I'm powering the 4349's with 300 solid state watts per cabinet which is more than enough for how I use my system.  Finishes include walnut along with the usual black.  Very heavy at around 80 pounds.  Sensitivity is 91 db and list price is a bit above $8,000 for a pair.

I feel that some of the Klipsch Heritage series cabinets have much more of a traditional horn and live sound to them vs. the JBL 4349's.  JBL did their homework on the waveguide to make it not sound like a horn though high frequencies will extend into the room with great effect.

I have a decent sized listening space and wanted a system that filled the room more than a smaller/traditional box speaker system could.  The 4349's (and associated subwoofers) really fill the room at moderate levels and should I wish to really make the amps work, the system can reach nearly crushing sound pressure levels. But they also work very well at low listening levels.  I enjoy most all genres of music and the 4349's are effective on most anything I listen to.  As you can probably tell from my rambling, I really love these cabinets.

While above your suggested price range, the aforementioned JBL M2's and 4367's are also great choices (M2 being the flagship waveguide loaded cabinet).  The 4435's are a cool old school JBL cabinet that were well regarded in their day, not just in the studio, but at home too.  The single 15" woofer 4430's could be another old school option for typically less money, though they do not have the low frequency "oomph" that the dual 15" JBL 4435 has.

There was a listing posted 2 days ago for a pair of JBL L200b's for $4500.

Spatial audio labs they use the very good Beyma Big AMT horn tweeter-midrange 

and dual 10 or twelve inch drivers and a very refined open baffle speaker over 92 db and right in your price range, and 45 day home  audition.

I am a horn speaker fan, but the really nice stuff is considerably more costly than $10k.  But, the Cornwalls can be quite nice with the right tube amps.  Something like the Volti Rival is nice too.  Although not a conventional horn system, I’ve heard the single-driver (back loaded quarter wave) Charney Audio systems deliver terrific sound; I heard the Companion system which is way beyond your price range, but the sell less-costly models.   

I've heard and liked Volti and also Charney Audio both have speakers in your price range.

I got my Cornwall 4’s to behave better by making wood angle jigs screwed to the base risers of the speakers and screwed to my wooden floor. These jigs are aligned with the back wall such that measuring their leading edge distances to the back wall allows for them to be precisely angled in tandem from the back wall. Speaker angles are derived by measuring the outside toe-in speaker corners from the back wall, and the speakers are always in exactly the same plane relative to each other.

The jigs also can be slid laterally along the floor (and locked) at minutely varying distances using each jig’s built-in scale without affecting their distance from the back wall.. This allows for them to be precisely centered to my listening position at minutely varying distances while still being in exactly the same plane with each other. So, this allows for the speakers to be kept at precisely the same angle relative to each other and to the wall behind them and the side walls no matter how you move them.

I also made an added 3/4 inch plywood base that is screwed to the underside of the factory risers with a sandwiched layer of that rubber shelf liner sold at Home Depot, etc. This reduces cabinet resonances without over-damping the cabinet.

Cornwall 4’s are notorious for being very finicky about placement, and these measures have made that a non-problem. These tweaks have revealed to me the full potential of the speakers for imaging and soundstage though they are still not "champs" at that.

I was thinking in these terms, wanting horn-loaded to go with a 300B SET, and opted for Cornwall IV. They’re pretty good stock but become excellent if you upgrade the caps and resistors to VCAP Odam and Path Audio, respectively. There’s a long thread in which Don Sachs outlines the values and process. I also replaced the binding posts with WBT NextGen and damped the horns and woofer baskets with Dynamat Extreme. Really great speakers now.

I own the JBL 4367 and use subs high-passed at 60hz but feel they are pretty good without the subs. I already owned the subs. 
 

Anyway I have demoed the current LaScala and Cornwall IV several times. I feel like the JBL is a better speaker. It is smoother in frequency response (downward sloping treble in room). I feel like the LaSala has a lot more box/horn coloration than the JBL 4367. I found the Cornwall harsher sounding in the mids and highs than the 4367, with the 4367 just being more refined in all aspects. the bass on the 4367 is better than both Klispchs to my ear. It is very detailed and has good leading edge impact. The Cornwall is not bad in the bass, just that the 4367 is better. The LaScala is in bad need of subs, I could not enjoy them long term without subs.

The only real flaw of the 4367 is the somewhat narrow soundstage but I kind of feel that is all horns. Honestly and all and all amazing speaker I have zero plans to sell. 
 

there is a used pair of Volti Vittora on audio mark right now for $11,000 that look nice. I have never heard them but it looks like a higher quality build than the LaScala. 

@glennewdick --

From what you’ve outlined I’d suggest a pair of (used?) JBL M2’s for active configuration, with a pair of Crown I-Tech 5000HD amps with built-in DSP. To my ears the M2’s are the sonic winners over the other JBL models you’ve mentioned, hands down.

Or, perhaps even better than the M2’s try and seek out a pair of used (and now discontinued) Meyer Sound X-10’s. They’re actively configured with built-in amps and electronic crossovers. Dynamite speakers that don’t "sound like horns" either.

Shinjitsu has my interest. Take a look.

Ha why won't you buy black?  just wondering.

What about the Klipsch Cornwall?  To me, it's the best of all worlds. Or the Forte IV which i find phenomenal.  

With your budget, you can buy a set of Cornwalls/Fortes and something else and swap them in/out as you get the itch.