JBL Everest DD67000 vs. Avantgarde Duo Mezzo

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.  

The Avantgarde Duo Mezzo's are a work of art, they also have a broader frequency response than the JBL’s.
That said, with the wrong amp the ADM’s can have an in your face sound.
On the other hand I have found JBL’s to be .... well - sound like JBL’s.

I realize it’s a horse of a different colour, but if you’re going to spend that kind of money, at least give the MurAudio PX1s an audition. I have yet to hear a speaker that sounds as life like, transparent, and dynamic as the PX1’s, not to mension their broad frequency response. In other words "real". You can also save yourself $10 grand with the MurAudio’s over the JBL’s.

Having is having owned Duo Omegas since the last 10+ years. And having heard the Duo Mezzo's often, the Everests 67000 are ahead of them. Just heard the JBL's on the weekend gone. 
The drivers have less distortions in the JBL, than the Mezzo's. 
Chise your amplification carefully with the Mezzo, as they are very unforgiving. But you get that right and you can be in sheer heaven. 
Similarly the JBL's will need more power and depending on your preference an OTL or solid state low distortion amp will get you there. 

Good luck. 

Regarding the Duo Mezzo's, would they be too much speaker for a 13x12x8 room? Would Shindo D'Yquems (18wpc) be a good match for them? Do they play all styles of music well, i.e., Americana rock, Afro-Cuban, Classical, acoustic Jazz? Thank you!

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).