Only a few have heard them yet. I am expecting a set for review very soon. There's great potential but they are for a defined domestic application in their present form.
I haven't heard them, and I have objected to some people in the past saying how revolutionary these speakers were, better than everything, while not overtly revealing they are dealers. That being said, if you go over to www.audioasylum.com a user by the name of "John Ashman" has posted NUMEROUS reviews and observations from magazines and other reviewers. He would be happy to answer any questions you have. Also, stereophile in their CES coverage called the NHT system the most improved, as they weren't totally taken by the initial listen last year. the absolute sound rated them the best system under 5k, or something like that. Go to audioasylum and ask john, he has many reviews and insights, as he has heard them.
Yes, John has been rather vocal about the Xd speakers. :-)
I have some reservations about the use of metal tweeters, but I haven't heard them yet.
There's certainly a lot of potential there, and it's cutting edge in many ways.
There are a number of speakers I'd like to hear, and I'll admit that the Xd's are at the top of the list.
I bought 'em - they sound absolutely terrific. I had a party two days ago for the brass section of the Los Angeles Philharmonic, and jaws were hitting the floor as they listened to these things. Stopped people in their tracks, literally.
Go hear them if you can find anyone with a demo pair (good luck).
Until recently I was a partner in a stereo store so I first saw them at CES in 2004, but they were just mockups at the time. I was using NHT 2.5i speakers bi-amped with a Arcam Alpha 9 and NHT SA-2 amps. I was going to upgrade to NHT Evolution T5 speakers with a Krell KAV-400xi. This spring I heard the Xd system for the first time at a dealer show and bought the demo pair on the spot. The Arcam made a terrible preamp with the Xds, I could hear floor noise from across the room! I picked up a Jeff Rowland Consummate and have enjoyed the music ever since.