JBL Everest DD67000 vs. Avantgarde Duo Mezzo

It’s lovely choice to make. I’m not sure the Everest can be driven by the usual SET amps- they are efficient but not crazy efficient. That would be the chief benefit of the Avantgarde, though bass integration has always been the trick: I have older Duos and have gotten them as good as i think they can be in that regard, save for having Jim Smith (the original importer and known set-up guru) spend time voicing the system. The Duo Mezzo with larger, horn loaded woofers may have considerably improved that integration issue, but, for me, on the older Duo, it was very tricky to get the bass to cohere with the mids- set for "good bass" in the room, there was discontinuity and set to match the horns, the speaker sounded bass-shy. (As I said, this may be less an issue given the woofers on the Mezzo).
I use relatively low powered SETs (Lamm ML2- not flea power) and the horn-SET combo can deliver magic on good recordings. The JBL is marvelous- not having heard the latest and greatest, but have heard the K2 driven by a ViVa amp (which as I recall was a lower powered SET) and it was wonderful-very in the room, no sense of a speaker, or system reproducing sound.
I think the JBL new is heavily discounted at least in the States, or seems to be judging by listings here. Perhaps it depends on where you are located; not so sure about new Avantgardes. Audiogon member Eberroth has a set of Mezzo Duos for sale here (I think he’s in Poland- don’t know him personally but know his name from audio stuff).
You should hear these things yourself- everyone is going to have their own preference; I suspect the JBL may be a little more coherent top to bottom but probably not quite as invisible in the midrange as the Avantgarde, given the two things: if the Duo Mezzo is anything like the older Duo I have, there is no crossover on the mid horn. None. So, hooking up an SET amp like the Lamm (which has a particular synergy with the Avantgardes), will give you a sound that has almost no barrier between the recording, the system and you on well recorded records.
You need to talk to the Great Karmeli (A-gon member DDK) who has some major antiquarian horns, JBLs and uses Lamms though I think he uses multiple amps for his JBLs, so your cost factor on amplification is doubled, if I am correct.
I was a Quad listener for decades, first the original Quad (which I supplemented, never satisfactorily, with ribbons and woofers) and later, the Crosby Quad. I switched to horns and SET amplification in 2006-7, and haven’t looked back. Very "in the room," alive, dynamic and don’t miss a thing in the midrange, which is always where I first get engaged or turned-off; if the midrange is boxy, grainy or sounds reproduced, that’s a big "tell" for me that the gear is getting in the way.
Take my observations for what they are worth- I think you have to hear them both with appropriate amplification and decide for yourself what suits over a range of recordings, not just a few cherry picked demo records.
One last observation- at least insofar as the Avantgarde experience is concerned- the speaker is very sensitive to associated gear and getting everything "just so" takes some time. (Perhaps that’s true of all good gear, but my system got progressively better as I upgraded gear upstream in the chain and spent time dialing everything in over a long term period).

gdhal- compared to conventional speakers, yes. My Duos are 104 db and the units with the so-called Omega driver are 106 db if memory serves. This may make the difference between using an SET amp or not. My ML2s, which are 18 watts each, are more than adequate for my Duos. I’m not sure they would drive the Everest effectively though. And the Lamm is not a flea powered SET. I know there are more powerful SET amps, includling Lamm’s own big dog SET, but you are getting into some real money with those. I did hear Magicos driven by the big Kondo SETs at a reviewer’s home -those are rated at 50 watts of output (I think), and they worked pretty well- but that amp is also expensive.

Gdhal, I have thought about the Everest as my next speaker simply because it is less involved than custom made horns with unobtanium drivers. I don’t doubt that the Everest benefits from some power, probably for the bass. I also don’t know enough about the X-over network to know how transparent it is, or whether it benefits from tweaking or bypassing in favor of some external one, but at a discounted price, it is actually not crazy money (at least compared to some of the uber horn systems and antiquarian ones). Hopefully, David Karmeli will weigh in here, b/c he has JBLs among other horns and uses them with SET amps. More later, and thanks for the kind response.

Right. As I mentioned, the issue of sensitivity bears on the kind of amplifier that can be used, and the SET is magic with the horns. However, at least with the older Duo, the issue is continuity or blending of woofers to mid horn. And the powered woofers are fed at hi-level inputs through jumpers from the output of the SET amp, so the self powered woofers are supposed to retain the character of the main amp. They may, but at least on the older Duo, you still have the horn v. dynamic speaker discontinuity in character I spoke of upthread. It can be ameliorated to a large degree, but it’s there. I’d have the same question if you bi-amp the JBL with different amps, but would be interested to know how that sounds.
PS: what external X-over has been recommended? The one thing I do like very much about the Duo (and assume it is true on the Mezzo) is the absence of any x-over on the mid-horn. I think it contributes to the speakers "un-reproduced" sound.  

I would think that Shindo amp would be great with the Avantgardes assuming you already own it. Room size- you don't need a huge room for horns, mine's larger than yours but you could get it to work- you'll probably be a little more "near field" than I like- my listening chair is about 13 feet from the speaker line, with several feet of distance behind me (along with treatment) and a few feet to play with at the front of the room where the amps and speakers are situated.
I don't know if set up is different for the mezzo than the older Duo, but there's lot's of advice on this forum about set up tricks, how to toe in, angle the speaker for your listening position, etc. One of the issues --since the woofers are integral to the frame holding the horns--is getting a position that gives you good bass in your room and also maximizes the stereo image.
As for range of music, I listen to everything from reggae, old blues records, early metal, hard rock, folk to classical and jazz.
The differences in recording quality will be quite apparent- but much of what I listen to is "standard" issue records from back in the day (admittedly, some quite recherché these days), rather than audio porn. In other words, you can, with good set up and associated gear, tap into the vein of the music- those lesser recordings still won't sound better than they are, but you will hear quite a bit of information. The trick is getting the system into a nice balance --i know that sounds like matching colorations--but you can get rich tone, very visceral presentation and horn dynamics without getting annoying horn artifacts or shrillness. One issue to contend with running speakers this efficient is noise- inter component grounding issues, for example, which won't be as pronounced on a less sensitive speaker. But, if you put it all together right, you will be able to hear far more musical information at relatively modest volume levels- you don't have to crank the volume control to get immediacy or vividness- it's already there (particularly if the recording is not a dog).  

2ndliner- I'd defer to Hornguys on your question. Jim was the original importer of Avantgarde in the States and a renowned set-up guy. 

Why don't you start an new thread, since you won't capture Shindo folks under this one? Just a suggestion to improve response rate, not an etiquette thing. I can also intro you to a guy I know in San Fran area who has Shindo and is in the process of evaluating various horns, including some custom jobs. Have fun. 

You guys interested in talking to Jim may have better luck emailing him through his Better Sound email address. His business, as far as I know, is to consult and provide on site set up advice for systems. There is a fair amount of info on him and his system on the web. 
bill hart

"Go by your ears; not what’s recommended by [a magazine].’"

This is a step toward wisdom as opposed to "knowledge."

I think Ralph is being modest - he IS atmasphere.