Well, the Beryllium cone TAD drivers were tremendously impressive (coincident source drivers), as were the less expensive, but close-cousin Aluminum cone (with Beryllium tweeters still) Pioneer setup.
Those sort of "rigid cone" drivers?
They were tremendously impressive in their own right - but after hearing the Bolzano Villetri earlier on, all I could do was pick and pick at the spatial flaws that are simply inherent in EVERYTHING, after hearing them. IN particular, I thought the soundstage simply died right at the speaker cabinets - width wasn't there... but that may be a function of the small room, not sure. They sounded significantly better standing up and as far back away from them as I could get (the TAD set).
SEAS never has complete units on display at CES - their booth always consists of a couple tables holding raw drivers for inspection.
On a positive note however, two years ago Dr. Wolfgang Klippel was demonstrating his complete suite of measurement tools, at the SEAS booth - and I had the pleasure of getting the entire enthusiastic presentation...
...and possibly the most flattering thing of all, was when HE tapped me on the shoulder in the car audio section, back at the main CES Las Vegas Convention Center south hall, recognizing me from the previous day - just to say hello. What a great guy!
If that's the sort of detail that you are looking for - the sort of thing you
might associate with a "rigid cone" driver - you are probably simply a good 3-way candidate.
I've been converted, after hearing some DLS sets - but I still truthfully prefer the detail of a good TN52... or even a JL XR tweet.
For good Focal mids though - you have to hear the K2Power. I truly love it - but mostly in smaller form, I'll admit.
A local Ontario competitor won IASCA finals, rookie division, Jeep Grand Cherokee, factory locations - speaker adapters for a 5.25" set in the doors.
I heard it once, and he gave me a real impressive demo... or I should say, it was just impressive.

The 7-series BMW I did, (and then transplanted to his new 7-series) used two sets of 4" K2P's, the rears with the tweeters robbed (oh, whatever AM I going to find a use for these tweeters for...

), and it sounded stellar with the Logic7 factory midbass speakers backing things up.
Small cone = rigid cone IMO, but without the potential drawbacks of weirdo tinny resonances...